Help with overclocking

[tigersty1e]

I have a BFG 6800 OC Agp card and I switched out the heatsink. The stock one was giving me 57 Idle and 80 load temps. The card was running extremely stable at these temps, so I know this card can get this hot easy. My new heatsink gives me 47 idle and 60 loads. A tremendous improvement!

I tried overclocking this badboy in the Nvidia control panel, but the system won't accept the settings. I try to move up 5 mhz and the system won't accept. Is the Nvidia overclocking program being extra cautious?

I have Rivatuner, but I don't want to screw anything up.