An EAA Webinar recently discussed two-stroke failure rates. It seems that the lowest rate of engine failure was in slow, draggy aircraft such as powered parachutes. Next highest was ultralights, followed by slow light aircraft such as trikes and Kitfoxes. Highest of all were clean, fast airframes. Seems that two-strokes can have a kind of lean-mixture runaway when the prop unloads, which is more likely in a fast plane (like a Dragonfly). Here's a link to the Webinar on Youtube: http://www.youtube.com/watch?v=GaaLb-BzqT4
I'd like to put in a plug for HKS: I've spoken with pilots who fly behind HKS engines and love 'em. Many of them flew two-strokes previously.

Wayne