Sweet benches by cmdrdredd.
Q9550 @ 3.8ghz + GTX670 > SB/IVB + HD6950 OC in GPU demanding games (which is most of the reason people buy a new GPU in the first place).
The exceptions are MMOs, strategy games and games such as Resident Evil 5, GTAIV, Dirt 3, etc. that benefit from a quad-core CPU (but Q9550 is a quad so this isn't as big of an issue like we are dealing with an E8400 here). But a lot of the times one can enable higher levels of AA or enable super-sampling shifting the bottleneck to the GPU. Q9550 @ 3.5ghz won't extract maximum value from a GTX670 but in games such as Batman AC, Metro 2033, Crysis 1/Warhead, Crysis 2, BF3 with 4xMSAA, HD6950 is choking.
Also, while Q9550 @ 3.5ghz might not provide the same minimums in BF3 multiplayer, HD6950 is lucky to get 30 fps avg in BF3:
The answer is: it depends on the game. Q9550 @ 3.5ghz is roughly equivalent to Core i7 930 / 860 @ 3.0ghz. It's not that bad. Nehalem had about a 15-17.5% increase in IPC over 45nm C2Q.
If I upgrade to Ivybridge or even Sandybridge now, I'll definitely skip Haswell.
What do you guys think?
I say get the GPU upgrade and get a full platform upgrade with Haswell. If the GPU upgrade solves your problems, you just saved yourself from getting IVB/SB.
Another quick way to test if the Q9550 @ 3.5ghz is a bottleneck in specific games is to lower its speed to 2.8ghz. Then perform the same test with Q9550 @ 3.5ghz and HD6950 at 0AA or 8AA. If the FPS drop with a CPU @ 2.8ghz is more severe, the game needs a much faster CPU. If HD6950 is choking with AA, then a GPU upgrade would be more beneficial.
Overall, with high level of tessellation and deferred MSAA in modern games, there is almost no chance that SB / IVB + 6950 will beat Q9550 @ 3.5ghz + GTX670 in FPS, racing, action adventure and RPG games @ 1920x1080.