I am also worried about the blending, but I'm thinking if I sacrifice the lm per area, I can place it further for a better blend. The T5s are probably way too bright to do a fair comparison anyway.
I'm using Arctic Silver Thermal Adhesive. It hardens and isn't elastic. It also binds things together for basically forever, so that might be an advantage or disadvantage depending on how you look at it. It's a little bit more expensive, but I heard good reviews about the brand too. I got mine off ebay.
Thanks for the link to the the spectrometer, I'll definitely have to pick one of those up.
Also, nice lights there. Are you going with 5 tristars or will there be more?