I've got a FSA Gossamer Mega EXO 50/34 and Ultegra 12-25 cassette. I've been riding for just two months and I did manage to drop the chain a couple of times when downshifting to the small ring. I was mashing too hard on the pedals; just a bit lighter and shifting's no problem. When I get around 3000 miles on the cassette I'll probably swap it for the 12-27 Ultegra; there's a couple of steep climbs where it would come in handy.
On most roads I'm in the middle of the cassette with the big ring; rarely go the small ring except on long or steep hills.
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