With a 4.350 bore the 4.5 stroke will have 535 cubes, and be all done by about 6200 rpm. The 4.375 stroke will have about 520, and may rev to 6400 max, so you shouldn't see a lot of differance. Cubic inch and stroke change are only 5.6 percent. If you find a smokin deal on either, i would go for it and not worry about the stroke. The power you can make with a 4.375 stroke is limited to your heads. Move up to a maxed out set of
indy 440-1 heads(the biggest you can run and still save your old pistons) and you can hit 900 hp with the right parts.