This THG benchmark has the 5870 at over 60 fps at 1920x1200 with no AA, max AF. Of course, it's with an i7-975, but I wouldn't expect to see an insane difference in fps vs. the X4 955. This Anandtech comparison shows the two processors pretty close except in Far Cry 2.
And I'd agree with MadAdmiral, that's basically the best gaming setup that you're going to get for $1000. That's an excellent build.
For further info, I'd suggest googling "5870 gta iv benchmarks"
I wasn't saying you shouldn't focus on FPS, I was asking why you just pulled 55 FPS out of the air. Most people focus on playable rates (30 min or 40 average) or the max that can be seen on a monitor (60).
Again, the X6 isn't going to do much for you. I would just stick to the 955.
Well , for me , under 45/50 fps it's not really playable it's almost impossible to enjoy the game , unless it's the most demanding game ever i can accept to run at 30 fps etc.
and i know about the x6 but i think i wouldn't feel right in my mind if i don't buy it , i'm planning to keep this pc at least 5 years , so maybe some games will need 6 cores soon , and even if it's not , i'd prefer to have it.