SystemSix is fantastic (52 cm), by far the best descending bike I've had in a while. I'm still out on the Tsunami (identical geometry with two 1 1/8" headset bearings and a tried-and-true Reynolds fork) - I think my wheel and tire choices are compromising its cornering at the limit.

Fastest ever was my Specialized M2 S-Works frame, but I never did many switchbacks with it.

Based on other bikes, I think that a stiff fork, solid head tube placement (i.e. not much flex), and a nice forward position (longer, lower stem) really makes for a nicely descending bike. For me it's been about weight up front - if I don't have enough weight up front, I don't feel secure, esp in turns.

After stability in a straight line, the most important part with a descent is turns - if the bike doesn't turn well at 50 mph, it's not going to be very confidence inspiring.

cdr