I recently bought a used road bike that has Ultegra 6510/9 speed shifters, a Shimano 105 front derailleur, Ultegra rear derailleur (jockey wheel cage plate is 4" in total length--medium cage?), standard FSA double crank. The cassette on this bike is a SRAM 11/34 9 speed. The bike shifts great except for the fact that it won't shift onto the biggest gear on the cassette. A mechanic told me that's to be expected since the Ultegra shifters are designed for maximum 27 or 28 tooth gear on the cassette. I would like to get a Shimano cassette in the 11/28 tooth range but most that I see on eBay are 10 speed. Will the setup that I currently have on this bike accept a 10 speed cassette or do I need to stick with 9 speed? I don't want to start changing out rear derailleurs, and the chain I have is practically brand new (SRAM 9 speed). Advice appreciated.