If you're getting up to 25fps in any of the benchmarks in 3DMark05 then that seems about right.
What is your overall score? For comparisson I get 5940 with a 3.6GHZ P4/2GB RAM/ATI X800XT card and in the individual tests maximum of just over 30 in test 1,mostly under 20 in test 2 and a maximum of just over 40 in the last sea monster test(mostly around 30fps though)
As for pc pitstop.........I wouldn't worry about that.Especially the 2D score.Your Nvidia graphics card by default reduces its clock speed when in 2D mode.This can cause confusing benchmark figures.
In any case you need to be careful about using benchmark figures......try looking at reviews of a 6600GT on the web and compare your 3DMark scores with those.I think you will find everything is fine.Try click here for starters.
A 6600GT with an Athlon 4000+ gives a score of 3681 in 3DMark05.Your score will be different due to different drivers/cpu etc but that is the sort of level you should be getting.
And as for the defrag speed.....if that was the first time after installation it is bound to be slow.A great deal of data has been put on the hard drive and needs organising.Try running defrag again and see how fast it goes second time through.
Run Sisoft Sandra again......give it plenty of time and don't move the mouse while it is working.It can lock up from time to time.I think it can get confused by background running programs.