What pads are you using now? I found that upgrading pads, fluid, SS lines, and the master cylinder brace helped tremendously with braking response and feel. They certainly stop faster over stock, as my OEM pads were almost completely shot.
Anyway, all of that will cost just a few hundred bucks, so it might be worth a shot before you spring for new calipers.
As an FYI, I have Hawk HPS pads (but I'd recommend the StopTechs, personally), ATE SuperBlue fluid (fantastic), StopTech SS lines, and Grimmspeed brace.