Alright, here's a bit of info for ya...
The 50W kit, only comes in 6000K, and has the dual element. price is 379.00
the 35W kits come in the full range of light output, but there are 2 types of Ballast: the slim ballast ($319.00) and the regular ($279).
I can't tell you about the difference in bulb life as I only have the regular 35W kit, but I do have them in projector lamps, both fog and low beams. I have left my highs stock, just cuz I disn't want 3 hid ballasts as I have separate High sockets. As for how they perform, I'm VERY happy with my 35W kit, just allow for the start up time, about 5 seconds (typical for ALL hid), a bit longer when it's really cold, and you're golden. Most projectors don't use a standard bulb size, I know my lenses require an H1 for lows.
Oh... and AAC's having a black friday phone in sale...