magic-sculpt is good for larger things. (100mm+) at that size greenstuff starts to work against you, for polymer clays I tend to like Fimo more than super sculpey for things under 100mm, but for over 10cm-30cm I find a mixture of Sculpey Firm mixed with Sculpey III works the best. Sculpey Firm by itself is a bit 'crumbly'. But Sculpey III is too soft and 'sticky' to be used alone. I often wonder what would be the results if epoxy clays were mixed. Im yet to actually try.
One day perhaps...