Don't need more gravity than will hold the fluids in
Widmanstatten crystal structure of Fe-Ni meteorites is a classic crystal intergrowth pattern, on scales up to hundreds of metres*
* why do I say "hundreds of metres", when we don't have any meteorites this big? - well, you can work out the minimum bounds of a regular crystalline system from the CURVATURE of the crystal shapes and the change in shape/ratio over distance.
* plus, we can calculate from models what cooling rates are required, and we end up with km- to 100-km asteroid cores...