so technically unless you've overclocked your cpu from stock settings it's either 2.0ghz or 2.4ghz (cant remember exactly what the 3800+ is but it's not 4ghz) also newer technology behind the processors is what makes them better not necessarily the ghz in which they run at. if you want to know how much better a cpu is than yours find some comparison benchmarks
Voxus: Even though you aren't going to get a performance boost out of more than two cores if you are just playing a game in a test environment, you will get a small boost in real life. This is because all of the background processes. When I play a game, I often have a few other programs running, like mIRC, firefox for looking up a guide if I get stuck, xfire, steam, all that random background shit. And since I have 4 cores, those things can hang out in core 1, while the game takes up 2 and 3, for example.
technically if he wanted to voxus he could disable all other cores to those programs making 4 cores run for gaming but only one core out of the 4 deal with the background processes (i think they have a program that can do this automatically)