Yeah, pics please Hirohsima. Yes the white stuff is heat conducting grease.
U bin goes from 90-120lm @350mA, a big range. SSC split it into U1 and U2 so the U2 will be 15% brighter than a U1. See the sticky here. X2 is T bin. I would buy from someone other than DX, I get a bit of stuff from them but for the LEDs you don't know what bin they really are.