I'm thinking about changing my rear cassette also so I hope the OP doesn't mind if I post here instead of starting a new thread.
I currently have a compact front chainring and 11-23 rear. I'm getting ready to climb close to 20,000 ft in two days and would like to put in a 11-32 in the back. I know that I'll need to swap out my RD in order to use the 11-32.
Will my SRAM Red shifters work with a APEX RD? What chain will I need to use for this combo? I'm using a Red 1090 chain.