Last year when I ran the 1000 I passed (left?) 4 bikes that were SOL because they were having lighting problems. I have an 8" HID and like the helmet light to fill in the spots, but it is a luxury. I will however say that after stopping to help all 4 of those bikes and leaving them in the night I was very happy to have a viable backup if something when wrong on the main system. On the 990 an electrical failure may be less likely, but once the lighting goes, it gets evil dark out there.
Good luck on the big bike. Make sure to share your spot. I definitely will follow.