I haven't found a single "kit" that is worth the effort to build. No single vendor offers the best of everything, let alone packages it all in a single "kit." In my case, I did my research into emitters first and found that the only way to get the spectrum I wanted was to use a mix of LEDs from several manufacturers. At the time, StevesLEDs had everything I wanted but they no longer carry any Cree LEDs at all so if I were to do it again, I'd need at least 2 vendors for the emitters alone (or just use more Luxeons and skip the XT-Es, which would be my choice in hindsight).
Heatsinks and drivers were another story. I chose to use LDD drivers which were not available at the time from any of the usual vendors, I had to get them from an "electronics supply" type place. I got my heatsink from another source since I didn't like what was available from Steve's.
I'd say, skip the kit and buy the parts you want separately. You'll be much happier with the finished product if it isn't made of compromises just to simplify the ordering process.
