Some programs show big differences on processor speeds why

Ok I have a Dell 530s (I know) well it has a intel 440 2.0ghz processor.... Vista crashed the first week I had it after trying to install service pack 1 and had to reinstall windows... I got cpu-z and it shows that my processor is running a 1995.varies but when I open performance test 7 to run a benchmark it shows the speed @ 1084... what gives are they both right and have a different way of showing it? Out of curiosity I downloaded cpu speed tester and it ran the test and the processor ran at 2054...

Before the crash performane test 7 always showed the processor speed at 1880 or so... Did reinstalling vista without all the junk dell crap hurt or improve the speed?

Oh one more thing I have 3gigs of ram and windows shows it most test show it but some ram boosters and cpu speed tester show I only have 2gigs?

Thanks ahead of time...

Mike