I have done some undervolting and overclocking to see what happens with temp and hashrate.

core i7 920 @ 3.0 GHz, 6 GB RAM @ 1600 MHz
GTX 580, 3 GB 384 bit, Core: 844, Mem: 2055, Shader: 1688
-i 0 -H 1 -C 1 -l F16x16
307.11 khash/s | 74 °C

Would it be helpfull if I try to compile CudaMiner myself for Fermi Kernel?