I just recently bought a 5906 and that thing eats ANYTHING! I guess I was basing my Q?s on that.
Those are nice guns. I drooled over a 4506 at my LGS for probably a month or so. They were just a little high on the price ana with as big as they are I kinda fell out of love with the idea of owning one.
Anywho I think the barrels on those are about 4 inches, I don't know. Probably a 124 grain would do well. Really any good quality JHP should work, you'd be hard pressed to find the best load out of your gun without doing ballistics testing from it. Even bullets of the same weight from different makers would perform differently.
There is some good info in the link below about standard handgun calibers and terminal performance and even has a list of specific ammo to look for.