I've had extensive experience with the Whites Fusion (but not the newest Fusion one), and although great flexibility and versatility, it wouldn't be my choice for cold water diving (We hover around 30-32F here in the winter, 60F in the summer). Not sure what your temps are, but I think it would suit warmer temps just fine (50F and above) with the bullet skin, not the sport skin. It was great in the summer here. Also found the boots weren't warm enough for our waters and used the Bare Cold Water boot over top the soft boot. Can't help you on the SP, sorry.
I dive the Bare XCS2 and find it acts just like a shell trilam suit (like the Fusion), but with the warmth properties of a compressed neoprene. Great flexibility and stretch as well.
Good luck!
---------- Post added March 24th, 2013 at 09:40 PM ----------
The Fusion undergarments are second to none, though!! SUPER warm!