I've found that the Tamiya Quick putty sands well if left to dry for a day. It's even a bit brittle rather compared to my rubbery old GS.
The Space Orc is based on this one, so it's deliberately not orky. I wanted to use rounder shapes and a more space-suity, haphazard (asummetrical) armour. I do like the round shapes and less junky look for the Orks. That's how the Paul Bonner Orks that I fell in love with back in the day looked.
Today's progress (still have a few hours of painting left.). Painting it proved a useful lesson, since I noticed where I had made good edges and not more easily, and which surfaces were actually smooth.