If the projectors were not designed for an arc-discharge lamp, do not install an arc-discharge lamp (essentially, do not install HID kits). It will mess up the beam pattern and you cannot accomodate for it by reaiming.
The only road-legal HID wattage is nominal 35; color temp should be nominal 4100-4250K.
8000K would be particularly horrendous: It creates irritation glare but does not improve seeing.
A better investment is installing a set of
relays, and getting the best H7 bulb you can get for the low beam. For stock wattages (especially if you DON'T install relays), get the
Osram Nightbreaker +90 or the
Philips X-Treme Power. If you do install relays, you should be good for these
Osram Rallye 65W bulbs.
If your vehicle uses 9006 bulbs for the low beams, then the
HIR9012s will fit (with a base modification).
If you have a 2004 or 2005 Celica GT-S, then it already has HIDs (using the D2S capsules). Stick with the stock wattage and color temperature, and make sure they are aimed properly.