Chris - having not yet ridden the FS (pedals went on last thing yesterday, and still no front brake...) I couldn't say. It's the seatpost out of my old HT (minus the shims). I think that the angle of the seat tube on the FS is such that it's going to put more sideways stress on the post than actually using the suspension of it, plus with the air shock it's not exactly necessary to have a sprung seatpost as well so can get something a lot lighter.
What got me about the geometry of the FS is that the bottom bracket is so high... it's about 14" off the floor! Still, at least the geometry of this frame is set up for this sort of fork (whereas my nail trail was rigid front end geometry with a 75mm fork), so things should work fairly well.
Something interesting I have discovered is that I can't have the horseshoe booster fitted on the back brake because as the suspension compresses it bangs into the seat tube. Unboosted maguras are generally a bad idea (flex, flex, SNAP) so I need to find some sort of lower profile booster.