your RAM is gonna limit you, but for reference (using XMS pc3200 or high performance ram), barton 2500+ easily gets to 200*11 (2200 Mhz) and 2600+ (according to many online reviews) gets to 2400 Mhz. with those speeds, the 2400 Mhz chip is far faster
EDIT: also, price should not be an issue, as the 2600+ is only $3 more than the 2500+ @ newegg