Nice motto, although I'm certain that my FPS was a constant 60FPS throught the game (1080p, max settings), with one notable exception of a "hideout" exploding causing huge lag. But the rest of the game was very smooth, and I'm only using a GT 240 as I said. I also have kept a very close eye on GPU usage via Afterburner and in the most intensive games it's rarely averaging more than 30-40% usage. Understandably then you'll see lower peak numbers but MOST of the time it won't make a big difference.
All that said, it does go to show that ~200 CUDA cores is going to deliver optimal performance. So GTX 260 or GTS 450.