Other than a few odd and ends those bikes are all very simular...pick the one that fits you best and you feel the best riding on.

The diferance in what parts they put on those bikes is small. You can tell that by the price . Unless we are talking about picking from the shimano xtr line and a Shimano M442 it doesnt really matter much.

If it was me id take the 6500 , thats just my opinion though. Any of the bikes you have listed there are good bikes...like i said up top just get one that fits you and fits you well.