There are a couple things, other than RC, that the 50ES has over the 30ES. First of all it's going to be quite a bit brighter. This in turn will give a much better 3D picture. They've also fine tuned a lot things software wise so that the 3D performance will be better over all. The Darblet has a more subtle effect compared to RC at most settings. Some people give the impression that RC typically blows picture artifacts (like film grain) way out of proportion and can give the picture an over processed look. This is why people typically keep the RC on very low settings or keep it off when watching something with a lot of artifacts.
I don't know what screen size you have, but if you have something larger like 120"+ I'd go with the 50ES because it's that much brighter. The 30ES should be fine for anything under that size unless your screen has a particularly low gain.