why not just get the new PIAA halogens? they output is alomost as high as HID (~6000k). i have 4000k PIAA on my car and they work pretty well. i havent been able to find the newer one though.
Color temp (4000K, 6000K, etc.) has nothing to do with brightness. Color temp is just the color it puts out. The higher the number the more blue/purple you get. Lumens is actual measure of light output. And I believe HIDs have 3X to 4X the output of halogen bulbs. Plus they run at a lower wattage (35W) plus they last longer than halogen bulbs too.
For me, I run HIDs on all my bikes cuz I like riding at night, its more functional IMO. If you really want the most output, get a 4000K HID kit for your bike, I had 4k on my 04 R1 and riding at night was a dream! If you want something more stylish get 6000K for a bluer tint. I wouldn't go anything over 6 cuz the trade off in light output doesn't make it very beneficial IMO.
Does your bike have projectors or a multi-reflector? If you have a multi-reflector your benefits of going to HIDs wont be as great if you had proejectors. Projectors can control the beam and light output much better than reflectors. I noticed that the HIDs on my gixxer (reflector) were better than halogen but not as good as my R1 (projectors) so if you can install projectors as well. Also if you have a reflector setup, it can blind on coming traffic if you dont get the correct bulbs.