Originally Posted by RubeRad

RD capacity estimates are always conservative, you can stretch them. The two limitations are chainwrap (tooth difference between big-big and small-small) and whether the upper pulley will be bumping against the big cog. You can try to correct the latter using the B-screw, or getting a longer screw with the same threading from any hardware store. I suspect you'd be able to get your current RD off of an 11-36, but whether your current RD (mid-length cage?) can handle (46-36=10) + (36-11=25) = 35 tooth chainwrap, I don't think so. You'll almost certainly need a long cage RD for that, which means mountain, and in the 10sp era, you gotta worry about whether mountain derailleurs are compatible with road shifters in terms of cable pull.