one other thing if anyone else is thinking about this sort of bike, i spoke to spesh USA, they hardly make any of the SX supercross frames and they are currently sold out globally, you need to order one in about june to get hold of the next years production which is usually out late summer.
And some frame weights for super slack micro downhillers:
nicolai ion 14 3.5kg
pivot m4x 2.8kg
YT play 3.3kg
Specialized SX supercross 4.1kg (i think this might be with shock included)
so the YT stacks up pretty well, even if it is the cheapest one