going on a 95 Accord, bone stock F22B2 minus a 4-2-1 manifold. only future mod may be an F23 w/ A6 head if this motor ever does happen to blow (once again, no more than maybe 150hp) what would be the better choice? 2.25" or 2.5"? pros and cons? or does it really matter?

 

2.5'' should be fine..

 

Ideally, you want the piping to match the header outlet diameter. When exhaust moves from one size pipe to a larger size, it rushes out to the sides to fill the larger pipe opening before moving out. This creates turbulence that decreases the speed of the flow of gasses and can add undesireable reverberations in the exhaust sound.