First off the 12.?? drivers are not what you want for a TNT2 card. Try the 5.?? series drivers. These are the fastest drivers for the TNT cards.
Then use either Powerstrip,NVTweek,NVMax,or TNTClock to overclock your card.
The Detonator 3 drivers are not optomised for the TNT series cards and actually slow performance. Try Detonator 2's, I think the 5.x series are the last of the Detonator 2's.