I'm fairly new on here, so I can't comment on the other kits mentioned, but since you mentioned Xetronic, I have ran them on my last three motorcycles (conventional on my '02 GSX-R750, and digital on my '08 GSX-R1000 and current Busa). The ignitor/ballast combo (if you go digital) unit is pretty stinkin' small, and I'm impressed with Xetronic's ability to make two bulbs of the same temp range match (yes, I've seen kits that actually varied, looks tacky...I'm anal about detail
). Ran 8000K previously (they don't light the road very well as many have mentioned here), and am running 4300K on the Busa. I've seen a few kits on bikes here in town, and once you hit 6000K the colors start to vary depending on the kit, although I guess they shouldn't IF they are all really at 6000K. I've also done some comparison of various kits, and lumen output varies by brand, even at the same temp range. I've abused my Xetronic kits over the years and they have never failed me nor have I ever had a misfire. I would recommend installing a relay regardless of what kit you order, whether it's a cheap kit, Xetronic, or one from XenonKing, you want to protect the investment.
Also, a BIG perk is that reflective markings on cop cars show up bright as day with xenon light from a good ways off, so let 'em try to hide on the interstates.
--EDIT-- To address your concern about blinding people, I aim the housing down a smidge, then let them deal with it...although I have been debating on creating a vynl "visor" of some kind as I don't want to hack my housing up to install a projector in the low beam area. We have a vynl plotter at work, so I'm trying to think of a way to make it compliment the bike and not look like some half-ass sticker job to cover part of the headlight.