I run 11x2.5" drums on my Challenger and Duster. The 11" drums do provide more stopping power, although they are heavier. I swapped the Challenger over to the 11" drums after I upgraded to 11.75" rotors up front. The 11" drums are a better match for the larger front rotors, which is also why I added them to my Duster, which had 11.75" rotors and now has 13" rotors from Dr Diff. Both cars use stock prop valves, and the front/rear balance is good. I haven't tried running the 11" drums on the back with the smaller stock rotors up front though, I always went to the large rotors up front first.
Parts for the 11" drums are readily available, maybe not quite as prevalent as the 10x2.5" brakes but I haven't had any issues fining what I need for them in the way of drums, shoes, or hardware. I run the large finned 11" drums, they do a better job of filling up my 17 and 18" rims than the plain style as the outer diameter is a bit bigger with the fins.
