I guess I have just been stuck on this quote from you: " I want the bottom end torque of a big block and peak power at 5500rpm…"
At that rpm head flow isn't going to be a problem. At bottom end of rpm range a 4.25 will definitely be badass. I didn't know it was available off the shelf. A 4.25 stroke with a 4.060 bore will actually be a 440 :)