Thank you for the link, SadieKate, I hadn't found that at Sheldon's site. It clarifies some things, yet still begs some questions.

On an intellectual level, the chart confirms what I've read and was told about gearing by one of the bike techs I talked to. But...

Today I was riding in the 48/25 which put me in a cross-chained position, but it felt fairly good. It gave me the perfect cadence and ok speed. When I realized I was crossed and switched down to the small ring, I went through both the 34/17 and 34/19 combos searching for something that felt right. According to Sheldon's chart, both of those combos should have felt similar to the 48/25, but I didn't feel anything in the small ring that seemed at all the same. Maintaining the same cadence in the small ring was more difficult (which I know doesn't make sense), and I could not maintain the same speed I had in the big ring.

So the question then is: Do I go with what I "know" is right, or with what I "feel" is right? And if I go with what feels right, how much am I going to mess up my drive train?

Which was answered by Deb, and I experienced exactly what she described. One of my bike techs had advised me to stay off the last two gears opposing each chain ring, which I've tried to do until today. With all the dust on the trail, the drive train ended up getting very noisy, especially so when I moved into those "forbidden" combos. When I dropped the chain, I stopped to fiddle a bit and could see exactly what Deb mentioned about the chain angle. The chain veered very obviously from the pulley.

So, the answer is: I definitely can't cross-chain because it will over-stress my drive train.

Which brings me back to: Any recommendations for a larger cassette? Or am I just crazy? (I think there was another thread with a cassette conversation recently. I need to find that...)