Today I modded the OTR 311 ! I changed the emitter/MCPCB.
So, I took the XML2 U3 1A (cold white) and put a Luxeon V2 4000K in a led4power MCPCB.
The original PCB is ~16mm x 1mm. So, when I changed the MCPCB, it rose the reflector up.
I needed to change the original o-ring and put a thinner one (below the lens) so that the bezel could screw in correctly, without gaps.
The beam improved, but clearly this OP reflector seems suited for larger emitters. Still, the tint of the 4000K Luxeon V2 is great on it 
BEFORE
AFTER
BEFORE > AFTER
