4.15 stroke may make for some really short pistons. might have oil control issues and want to rock in the bores some. 4.15 should provide more torque than the 3.75, if you like the 3.75 stroke kit before use it again. not a really high revver of a high power engine stopping at 5800 rpm. so the shorter stroke with less problems would get my vote.

does the 4.15 crank use shorter rods?