First I would test ride the bikes and see how it feels, If it flexes under hard pedaling , you might want to consider aluminum. I weigh 240lbs (I started out at 275lbs last July) and I prefer aluminum since it is flex free for my weight. I have a Trek 1000 and so far it has held up to my weight without to many problems, I only had to swap out the rear wheel from a Alex AT-450 to a mavic deep dish CXP 30 rim so I would not lose any more spokes.