I have two evga sc 750ti, with one of them I can't push the GPU beyond +91 / 1410mhz but the Mem can go as high as +750 without crashing.
The other card I can go up to +130 GPU and +500 Memory.

For cudaminer I find running the x86 version produces a few more hashes. -l T5x24 seems to be ideal for scrypt mining. Also try running Chrome with something like the youtube homepage loaded and see if you get better results.