Super D is a blast! Did my first one this year at the Schweitzer National. It is like the fastest fireroad bomb you've ever done - with 20 other people around you. I come from DH, but I was WAY overdressed and oversuspended for it. A 4-5" dual suspension XC bike with 2.35 tires would be perfect. If it's a hot day, wear some light DH armor without a jersey (after all, you WILL be going fast!). You want protection without bulk. Practice "flattracking" corners (foot down, sliding sideways, sans brakes); you will gain a lot of places if you can corner fast. Try it for sure. Good luck!