HD 5870 Two Way Crossfire Power Supply Question

[Pirs01]

Hello,

Hardware noob here.

I am looking to upgrade my old ass system with new gpus and have a number of restrictions:

1. Budget - it's low.
2. Mobo chipset - AMD 790GX. According to this chart HD 5970 is the highest I could go if wanted to Crossfire.
3. PSU output - Corsair VX550W.

Based on my research I decided my best option is to get 2 HD 5870. Based on this chart and this benchmark I should be looking at a performance somewhat comparable to that of R9 280X or GTX 690. The 5870 are a pretty good value.

They are perfect fit - almost. The official spec says 600W supply recommenced for running 2 of them.

I am hopping to spend around 110$ for two cards so if I had to replace PSU for bigger one then my total cost would double or worse. I'm not willing to invest that much in this 7 years old machine.


TL;DR - So here are my questions:

1. With 600W recommended what are the chances it will run with my Corsair VX550W?
2. If it won't can I make it work by underclocking the cards?
3. If so then how much lower do you suppose I would have to go and is it still worth it?
4. Is it safe to try this setup with PSU potentially lacking the necessary power?


If I cannot or should not go Crossfire then I was thinking something like SAPPHIRE TOXIC HD 6950 which would be significantly weaker (3177 score for non - OC version) compared to two two 5870 (about 5200 score minus the Crossfire overhead). On plus side it should be even cheaper, it's a single card (I like that fullscreen windowed mode) and has 2 Gigs of memory. Other suggestions are very welcome.

5. What would you guys recommend?


Thanks!

 

[basroil]

That's an absolutely stupid idea. Just get the 280X/380 or even an overclocked 960, crossfire is a last resort, and anything less than a 7950 is pointless now that DX12 is around the corner. Hell, just get a 260/360 if you're on a budget

 

[Pirs01]

R9 280X / R9 380 - These are out of the question. Would cost me 2 or 3 times what 2 HD 5870 would. As already explained I am no willing to invest this much in this machine.

R7 260X OC / R7 360 OC (new) - Same 2GB GDDR5 mem. and slightly lower performance score then SAPPHIRE TOXIC HD 6950 (used) for twice the price and 25% more then 2 HD 5870. What would I be getting for twice the price? Only the new APIs support?


Let me explain further where I'm coming from. I will be building a new machine sooner rather then later and gaming is not a priority especially on this machine that will get replaced and then be used for work only. If I can squeeze more power out of it for few bucks then fine. If not then oh well, not a big deal. I don't need to be able to run games that use DX12 API and are yet to come out so I'm not sure that I care about the new APIs compability at all unless you can convince me otherwise.

Another perk of the Crossfire that I did not mention is that I can buy one card now and then buy another one some time later or not depending how happy I am with just one (still significant upgrade from what I have now) and when will I be planning on building new machine.


Since you did not justify your suggestions at all (other then DX12 compability) I still consider both HD 5870 Crossfire and SAPPHIRE TOXIC HD 6950 to be far better choices. I would appreciate if you would explain your suggestions beyond "that's dumb, spend twice your budget instead".

Thanks!

 

[basroil]

1) If you're going to use the machine for less than 1 year, don't bother spending a penny on it.
2) Don't think for one second that outdated benchmarks mean squat when comparing cards from different eras with different driver support.
3) The 5870 CF DOES NOT HAVE 2GB, IT HAS ONLY 1GB for programs to use (multiple card memories do not stack). With most games demanding at least 2GB to even run at 1080p, the 260/360 will be much better in new games simply because it can actually play them
4) You would have to be stupid to buy a graphics card now only to replace it when you upgrade in a few months. Just get the graphics card you would have put in the new machine now, and then put it in the new machine once you build it!

 

[Pirs01]

1. I may or may not build a new machine within a year but after I do I will keep using this one as mentioned before so an upgrade is in order even if I were building the new machine now.

2. OK. Good point about the driver support. Now I'm learning something.

What makes you think that these benchmarks are outdated? I mean we are talking about a 2010 card. I would imagine a good portion of them are still in use rather then in dumpster and so the datasets continuously fed into this chart should be rather decent no?

I looked up the HD 6950 vs R7 260X specifically and it looks to me like in theory the 6950 should be superior? 260 has some of the specs better and perhaps combined with better driver support it explains why in practice they come out roughly the same? Even if the 6950 were to be weaker, still we are talking half the price here. Similar story with R7 360

Two things I wonder about that the newer cards have better are smaller manufacturing process resolution and newer PCIe version. How much impact on performance these two would have? In my case my Mobo doesn't support PCIe higher then 2.0 anyway but it might be telling about the difference between the theoretical diff. in performance and the actual one from the benchmark chart?

3. Sure, I know that. Maybe most games that come out now need 2GB to run at all - I wouldn't know, I don't play them. The most modern title i play is Path of Exile that works no problems on my ancient 1GB card (except end game particle hell party of course) at 1680x1050 on low settings.

However looking up the HD 6950 just now I saw people playing GTAV on it with mid settings and that's more then I expected. I don't need even more power then that so I'm giving up on the HD 5870 CF for now. With 2GB V. Mem. the machine should stay usable for longer I hope and it's cheaper. Thanks for helping to turn me around on that front.

4. The card I buy now will not get replaced ever most likely as the machine will not get any more upgrades. As explained I will build new machine while this one remains in use for work probably till it ends up in dumpster. I'm not going to buy the card for new machine now for numerous reason that I will not bother you with. Probably best if we stick to tech and I can handle my financial planning myself but thanks.