I agree with regard to comparing Toda to DC. I do not know numbers, but I can tell you that the Toda is better quality. Not that DC is bad, it is economical.

As far as the exhaust is concerned anything from 2 1/4 to 2 1/2 should not really make that big of a difference with basic upgrades. With the 2 1/2 you will most likely experience more backfiring/popping/crackling noise w/a straight through design. At least that is my experience. With basic upgrades and a 2 1/2.