Originally Posted by
Little Darwin
....
Based on guidance I received from my bike shop, I needed a long cage for my compact double (50/34) with an 11-28 cassette. But I wanted one anyway, as it means I can choose whatever gearing I want without needing to be concerned with swapping the derailleur. ....
Funny, I have exactly that combo (50/34 and 11-28) and the short cage RD works fine for me. I specifically asked my mech if I needed a long derailer with the 11-28 and he said "no". He did look carefully at the chain length though, although he did not change it, as I was changing from 53/39, 12-25.