It would help a bit sure, but with the weight on the "bit" part, 2,3-3ghz on amd can give you full speed only if you're really limited by cpu and you lack like 10-15 fps to the max, some notes about those games - pretty much Shadow of the Colossus needs speedhacks on any cpu soo doesn't expect it would run smooth. Tekken would probably not be fully happy with just amd 3ghz either.
But world isn't made with just bad news, about DBZ:BT3, your current pc is more than enough to run it at full speed, probably including 2 player mode which is rather demanding mostly on gpu. If it lags it's probably only couse you have AMD gpu as radeons aren't loved by default, you can try using "allow 8 bit textures" in GSdx config which is pretty a must have for me with a bit weaker radeon for this game otherwise it always lags. And if it's trully limited by cpu, use svn version of pcsx2
, which decreses cpu requirements of this game by quite a bit without using any additional options.(I could confirm it running at 1.6-~1.7 ghz athlon II which is same fast/slow as phenom II cpu while in older versions of pcsx2 it needed around 2.4-2.5ghz for full speed) I also think allowing 8-bit textures could help on radeon cards in Dragon quest, through with 2.3ghz on amd you can be also cpu limited, maybe mtvu speedhack from svn version could also help for it as you have tri core cpu while pcsx2 without that new speedhack uses pretty much only 2 of them.
In other words, firstly try to optimize your experience on those 2,3ghz, couse a change to 3ghz and additional core which will be useless for pcsx2 will not really be such a big deal. 4ghz would be other story, but still don't expect SOTC to run smooth on it, it's just one of those game with issues. And if you just care about full speed without smoothness Shadow of the Colossus probably could run at what you already have if you abuse some speedhacks.;]