I have read where for every pound of pressure in the cooling system you can raise the boiling point three degrees F. So if you're already running a 15# cap and you go to a 16# cap I really don't see a big difference.
x2, I agree with mopardude, also if you have an HP motor be sure and run a 3 or 4 core radiator if you do any driving in town or get caught in traffic every once in a while! You'll be glad you did.
