Can I answer, even though I'm not mattc? I've ridden brevets on steel bikes (solo and tandem), welded aluminium bikes (solo and tandem), bonded aluminium bikes and carbon fibre bikes. The steel bikes included spaceframes, monotube frames, diamond frames, dual suspension, small wheels, separable and folding frames. Distances up to 1600 km. Is that enough Audax experience to form an opinion about suitable bikes?