The 4.25 has a 2.200" rod journal and is actually an easier build, the smaller journal will have a big positive effect on the bobweight. You're taking the equivalent of a .068" wall thickness, 2.375" OD x 8.2-ish " long (sum of the 4 rod journals) 4340 steel pipe worth of weight off the crank compared to a 2.375" journal. Then additionally theirs less weight from smaller bearings and reduced friction losses to that mix.

1 cube is worth about 1.3-1.4 lb/ft of torque on a good street stroker, so 15 cubes is 20 lb/ft across a pretty wide powerband.

Worry more about good heads, induction and cam, a properly machined stroker is going to make so much torque you're not going to needto wind it up very often, it's like a 44 magnum, it feels good having it when you occasionally need it.

The thing I worry most about with one of my bullets is.....Tire wear