Licensed Bike Geek
Join Date: Oct 2002
Location: Los Barriles, Baja Sur, Mexico
Posts: 1,360
Bikes: Look 585, Kirk Terraplane, Serotta Ottrott, Spectrum Super Custom, Hampsten Carbon Leger Tournesol
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Barry2, as I posted earlier; you have the 6700ss rear der already and you're going to use a 30T cassette. Why don't you try that combo as an easy experiment. Ride carefully and see if it will work to your satisfaction. If it does, it's a win for you. If not, change the rear derailleur.
I'm 78 and certainly don't want to be hurt on my bike. That said, I've been riding my bikes with a 32T cassette on my bikes with NO issues for over 5 years. Some of my bikes are off the rack, some are custom. They are made of steel or carbon or titanium. All are pretty modern, the oldest being a 2010 Look 585. All have a compact 34/50 crank. My point being that in multiple personal experiences, what I have works extremely well.
As another here has posted a Shimano 9-speed MTB derailleur is the best solution and will work with up to a 36T cassette with your existing components. This is a very common thing to do and used by many who tour and/or have many hills to climb.