Originally Posted by
nhluhr
RD-6700-SS (assuming you currently have the RD-6700-GS, the SS would work better in the double config, but the GS will still work)
I've never noticed any shift quality differences between short, medium, and long cage derailleurs on the same bike.
I could see the larger units wearing out their upper and lower pivots faster due to the added leverage, although the sixteen years I got out of my last medium unit was long enough.