Is 2GB of gddr5 enough for upcoming 8gb PS4 games?

wot.

Lol.. Why not, I'll throw out a very wild guess based on rumors.  

I'll guess that any PC with these specs will be able to run straight 'next-gen' console ports for the next 5-10 years:

1) 8 gigs of RAM.
2) A 7850 2GB (1.76tflops, 153GB/s mem b/w) or higher, OR it's NV equal.
3) An AMD 8 core of some kind, or maybe even the (amazing imo) 4-core i7's, but I'm not sure on that part yet.

In short, yeah I think most current mid-range+ 2GB cards will be fine playing new console ports (if the rest of the hardware can handle it).

I was more curious about the mem size. If the 2gs pc cards can deliver same image without noticeable streaming from RAM.

In that case, I'm with JJ1217.

wot.

I'll buy a 7850 2gb. Can i handle anything then?

No one knows what the next generation of graphics will need for video memory until they're out. If I were you, I would grab a card with 3gb or more just to be safe. Some current games on my system use upwards of 1.7gb of video ram playing games @ 1080p with aero active in windows 7.
300mb doesn't leave much room for possible true high definition textures that hopefully are coming soon to new games.

There is a difference between allocated vRAM and actual used VRAM.

EG, I use dual 670's at 1440p in Crysis 3. With no AA according to MSI AB I get 2037MB usage, but with 8XAA I get the same. See what I mean? Its way too stressful for a rig to constantly monitor real time video ram usage.

I believe the GDDR5 memory on the PS4 is for the memory and to be shared with the [rumoured] APU. It makes sense because the way APUs work is they use your system memory so the faster it is, the better the performance. It is also rumoured to have a 7850 level graphics. Or a [ever so slightly] slower version of a GTX 660. It should perform identical to most mid-high end modern day systems out there.

Actually OP your question is wrong. The real question is "Is 1gb of gddr5 enough for upcoming pc port of ps4 games ?

Far as I'm aware, the 8GB of GDDR5 in the PS4 is shared with the APU and the secondary processor (for background stuff like downloading and OS), so I doubt it will have more than 3-4GB actually available to the graphics engine.
The amount of VRAM does not impact performance until you run out of it, and at 1080p you quite simply don't need more than 2GB right now. I think Sony are just thinking long term by giving it so much VRAM.

After all, the current console generation has lasted 8 years, and who knows what we will see in 8yrs from now. My bet is that Sony are thinking of 2560x1440 and 4k TV's and monitors becoming standard, they sell a 4K TV after all and they are very quickly dropping in price.

PS4, according to sony will offer over 2 teraflops of computing power.

It seems like its just gonna be an 8 core apu that has 8gb of ram. nothing special on hardware but since its built specifically to only game and not run an OS, its gonna be pretty strong.