Can i overclock 8600 GT 512 DDR3 little bit more

[PAOLA]

I overclocked 8600 GT graphic card. GPU Clock is 643 MHz and Memory clock 923 MHz. the temperature at idle is 57 C and on full load is 68C-70C. Can i overclock it to a little bit more. Is this temperatures are normal ?

[MACY]

The standard GeForce 8600 GT runs at 540 MHz and accesses its 256 MB GDDR3 memory at 1.4 GHz (700 MHz transferring two data per clock cycle) thru a 128-bit interface, so it can access its memory at a maximum transfer rate of 22.4 GB/s.

[KADEN]

I read some articles about being able to overclock the 8600gt to a close match to the 8600gts. Most of these are the 256mb models I have the XFX 512mb versions with stock speeds of 540 core and 400 mem.