4gb HBM vs 8gb vram for future proof Gaming (2x390 vs 2xfuryx(Gemini))

I completely agree with all of this, though despite the fact that FutureProofing is like impossible to predict and how well it will do, I am an, AMD fan boy. Bam shocker! Anyways I would say go with the two furyx's, because I own a 390x which gets up to 60 degrees idling on MSI afterburner, then it will go up to 95 degrees on furmark with full fans which sounds like a jet engine. Thus I recommend the fury x due to the liquid cooling, if you have two 390x in the same systems you will have heat problems unless you want your whole computer to sound like a F-18 and still reaching high high temperatures, unless your fine with that and plan to game on 4k then go with the 390x just because more vram is helpful in higher temps, but the 8gb of HBM is alot better if your doing less then 4K. Goodluck!

0) Wait?
There will always be something newer coming. We don't have exact dates and pricing, plus it may take months to get a good non-reference card that's not sold out. Who knows, it could take six months from now. I say buy a card and be happy. I'm still rocking a GTX680 and not in a huge rush, though I do carefully tweak my games and that makes a HUGE difference (especially using Adaptive VSYNC... i think alternative is Dynamic VSYNC with RadeonPro for AMD users.)

1) 4GB of HBM is not enough IMO to future proof->
The memory sits next to the GPU and being faster (to the GPU) this does help a bit at higher resolutions due to minimal latency getting code in efficiently.

*However, if a game wanted to use 6GB of video memory that means there is 2GB that could be in the video memory but is currently NOT there. Fast video memory doesn't help if the data isn't even in it in the first place (already proven by PCPER in GTA5... the frame rate plummeted relative to the GTX980Ti at same settings chosen to give almost 6GB vs those chosen to stay just under 4GB).

(DX12 allows us in theory to add VRAM if we have more than one card, but that must be supported by the developer not to mention it's going to be quite a while until most games are DX12)

2) AMD vs NVIDIA:
Ignoring PhysX and a few other things, while I normally prefer NVidia I'm very impressed with AMD's focus on driver support for some things though it's not clear if they're going to improve DX11... though assuming a good Intel CPU the poor efficiency shouldn't make a huge deal AFAIK.

So... I prefer NVidia, but feel okay recommending AMD if the price is there.

3) FREESYNC vs GSYNC:
FREESYNC is finally usable with the new Crimson drivers. Good job, and the monitors are cheaper. I think it's close enough there for now to not go further. A few weeks ago I'd be saying go NVidia just for that reason (i.e. future GSYNC monitor).

4) Crossfire or FREESYNC monitor?
Right now it's roughly $600 for a 1440p FREESYNC, 4ms g-g IPS monitor that's 144Hz (the best combination of specs IMO).

I would strongly recommend if going AMD to invest in a SINGLE R9-390/390X then put money aside for a good FREESYNC monitor.

(maybe a $500 model in first half of 2016... the ONLY monitors I currently like are closer to $800. I'm confident we'll see a quality $500USD model with the specs above in under six months.)

Crossfire can give you higher frame rates, but you still have to deal with the VSYNC On/Off issues, not to mention FREESYNC can look smoother at lower frame rates which can negate most of the dual-GPU advantage.

*And FREESYNC works for ALL games, whereas Crossfire does not, and even with improvements is going to be a constant hassle (is it smoother with or without...) and of course noise and power.

5) Relative performance of GPU's (use 1440p):
https://www.techpowerup.com/reviews/MSI/R9_390X_Gaming/30.html

*GTX980Ti is averaging almost 30% higher here (varies by game).

**Price however is very roughly $650 vs $400 for comparable cards (USD) which is 62% difference, plus that's $250 you can put towards a FREESYNC monitor (which is also cheaper than GSYNC monitors right now).

Summary:
My advice without knowing your current monitor is this:

1) Buy a single R9-390X, and
2) Save up for a quality FREESYNC monitor with similar specs to what I mention (2560x1440, 144Hz, IPS 4ms)

I hope this helps.

Update:
*Get the latest Crimson beta driver if going AMD. Latest is I believe Nov 30th, and I think that's the one with the fix for the potential fan issue causing overheating in some cards.

atrix396,
1) liquid cooling can be problematic too

2) The Fury X only has 4GB which I've said is going to be an issue in the future which has been proven by testing GTA V.

3) The Fury X also costs about the same as the GTX980Ti, which is a better card in every way IMO.

There's not one advantage to the Fury X I can think of other than enabling a slightly cheaper FREESYNC vs GSYNC monitor. The GTX980Ti is incredibly quiet with the right model (perhaps more so if there are pump issues). The Gigabyte G1 is I believe the one Jayz2cent reviewed on Youtube and it was very quiet.

There's also things like PhysX etc that AMD doesn't have so for me the AMD card needs a price advantage but 6GB is my minimum for VRAM on expensive cards.

3) I'm checking the NOISE of the R9-390X cards and will post back, but the cards are excellent value otherwise.

Example FREESYNC monitor that's inexpensive:
http://www.amazon.com/dp/B00VBNQJKU/?tag=pcpapi-20

First off, that's ultra-wide (pros and cons) so let's look at the specs:
- 21x9
- 2560x1080
- 29"
- $335
- FREESYNC
- IPS 5ms
- 60Hz

If on a budget, this is a really interesting monitor though my main beef is that you are capped at 60Hz (60FPS).

The new CRIMSON drivers solved the low-end for asynchronous support, and I think (but can't confirm) that there's a way to GLOBALLY CAP and stay in asynchronous mode?

*I saw a video at PCPER where they pointed to the global cap, however from past comments I don't know if capping to say "60FPS" means you can stay in freesync mode or whether it's got to be somewhere slightly lower (I mean 55FPS would still be a great experience with asynchronous enabled).

I'd still strongly recommend waiting a bit and get a monitor with specs that I recommend (especially the 144Hz or at least a minimum 90Hz).

THIS represents my current IDEAL specs, however the quality is a deal breaker and I didn't see a similarly priced monitor with similar specs and same quality:
http://www.amazon.com/dp/B00ZOO348C/?tag=pcpapi-20

(very, very important to investigate quality such as average customer review score, and 1/5, 2/5 score comments as light bleed or other issues may be common)

I have the gigabyte g1 980ti, had it since it came out and runs like a dream, so far never heard the fans from it while gaming or stress testing/benchmarking, rund everything at 1440p highest graphics at least 60fps, apart from assassins creed syndicate which is 30

only issue I have with it is if you want the led's on the card to be a particular colour apart from the default teal it can be confusing to get it set up, you have to use the gigabyte program and nvidia experience led settings, then everytime you turn the computer on you have to open gigabyte again. Only a small thing though and has no impact at all on performance or noise, just aesthetics

Yeah all of them except grid, they all run at 60+fps at 1440p highest graphics, only exception is gta, I turn the anti aliasing down to 2x msaa and get about 70 fps usually. Seem to remember shadow of mordor was in the 90's havent played for a while and witcher runs between 60 and 80 fps