I've used power grips and like them. I'd be curious to see how they work in combination with your fivefingers and the duathlon.

A couple of years ago I posed a question to a triathlon forum about using power grips for a sprint (short distance) triathlon instead of clipless. I figured not having to change shoes in the transition would more than make up for any speed gains a clipless system would give you for the 15 mile riding distance. Overwhelmingly people disagreed.