I don't cycle with them, but I've used Crumpler's camera bags a fair bit (using a "Loyal Chap" currently to carry a D70 + 18-70, F3/F90x + 50mm, 12-24 and various lenses/body in the lower portion. Generally weight is carried well in them (straps take a long while to feel uncomfortable, even with that weight), and the stabiliser strap (crumpler call this the third leg) works really well to stop the bag moving around while being carried.
If the messenger bags are as good as the camera bags, they'd be a good bet, imo.