I am helping a friend do some upgrades on a Trek 2004 5200 outfitted with 9 speed Ultegra.
Would like to possibly upgrade to a Ultegra 6700 5 pc group (use existing crank)
1) Are there any issues with using the newer 10 speed chain with the old 9 speed crank (ie - tooth width, etc)
2) What is the difference between a 6700 and a 6703 lever?
3) Any other 'gotchas' to be aware of?