We do not recommend doing an HID kit for the high beam. HIDs require about 3-5 seconds to fully ignite to a usable level, then another ~60 seconds to reach maximum output. This means when you switch from low to high beams, you potentially have a deadly 3-5 seconds of near relative darkness for your eyes to adjust.
Some of vehicles may allow for high and low beam to be on at the same time. In this case, you would still lose any functionality of “flashing your high beams”. This quick "on/off" is extremely harsh on the ballasts and is not covered under warranty. Furthermore, using the HIDs in high beams is a relatively moot point as you would not get much more throw from the light… merely a slightly higher angle. If your low beam HIDs are of good quality and aimed properly, it would be extremely competitive to doing a high beam retrofit.
Keep the high beam your regular halogen bulb.
Of course, this is merely our opinion and the choice is ultimately yours.