Before I got my rift I had no reason to upgrade my g Card. Everything got 30+ FPS and if it did not I would lower setting a little.
After my DK2 arrived everything worked ok if I change setting, lowered details etc.
Example
I have
Desktop with ATI 5750
Laptop with Nvidia 1800M
Both can play HL2 at 75fps in the RIFT.
Granted the 1800M has to be overclocked 15% and "Windows Compositing" turning off but it can do it [just].
I tried this at a friends house and he had an old NVidia 8800 which could do about the same has the 1800M. He walked to the shop and purchased a 970 card for £260. He now gets 300fps in Hl2 (it seems to hit a FPS limit, sure it could go faster)
The G card are here NOW! the NVidia 970 is an amazing g card for the money. And it will run every AAA game at 75fps in the rift. If anyone complains that they have to lower the setting a little on a game to run on 970 in the rift, I would argue that with the resolution in the rift you would not be able to tell. I defiantly can not. And if you want the extra options, Buy the 980 [if you have £420 doing nothing]
All this before the g card companies do any driver optimisation for the rift. I have a 3d monitor and before driver optimization playing 3d games got about 50% the fps to view in 3d. With the driver optimisation over the past few years the it now gets 75% the fps.
I am sure that when CV1 arrives there will be a g card that will run everything at 90fps in the rift [and it will be less than £250].
Oculus may even Sell a bundle with the g card.
Imagine:-
Oculus Rift CV1 £250
Oculus Rift CV1 + Nvidia 970 [or the newer one at 22nm] bundle £400
Hooo Yea....
P.S.
Not forgetting DirectX12 which is 30% quicker and multithreaded [finally]
P.P.S.
I am actual going to get a 980M Laptop. [Always on the road but can not live without the rift]