GTX 260 SLI overclocking issues

When I went into Ntune and OCed both the core bus and memory bus (core by 20,mhz and memory by 25) the frame rates in crysis were about 5 fps worse. I don't understand it, especially because i was able to OC 1 gtx 260 to 709 mhz on the core and 1180 on the memory before games began to crash, the temps aren't bad either, hovering around 60 degrees while playing crysis

I have a striker II NSE board and the lasted chip set and GPU drivers

Running windows vista Premium 32 bit 4gb of ram, intel e8400 cpu