Don't get confused - the Y3 is definitely SMO, not OP - no doubt, 100% sure, etc... The X3's copper is the cheap kind sold at DX, FT, and other places - it's not bad though, better than aluminum. Here's the #'s I measured:
Yezl Y3 (from WB), on fresh EVVA KK cell: 2.50A tail, 830 OTF, 61 kcd (no issues)
XinTD X3 (from Group Buy):
#1 - 2.85A tail, 972 OTF, 47 kcd (reflector imperfections around the emitter - doesn't seem to effect anything)
#2 - 2.85A tail, 952 OTF, 45 kcd (not centered LED, quick drop in output noticed in 1st second)
The X3 is more pocketable but the heavier weight may be an issue to pocket. I see and read of more quality problems with the X3's for sure.
Here's some weight measurements I just did:
Yezl Y3 #1: 287g, Yezl Y3 #2: 290g
XinTD X3 #1: 300g, XinTD X3 #2: 297g
Stock HD2010: 292g
So, bottom line - Y3 at lower amps throws much better than a X3 (should be expected from the bigger reflector), but the X3 has more lumens because of the higher amps. The Y3 can take long batteries - I even fit 26700's, like the new KK 5000 26700 that test at 5300 mAh!! The X3 is short length cells only. Both are superior designs with a nice SS bezel, pill-less design, both have exc. heat sinking.
Though the Y3 is slightly lighter, I feel the heat sinking is located better. HD2010's for example have lots of wasted metal and thicker bezel which keeps the outer diam. large, but has a reduced I.D. of the reflector - not as optimized as the Y3.