I don't play that high (4-8, 6-12), but I have trouble believing that HE is a more challenging game, on a purely mechanical level. In stud, there are so many cards to keep track of, so many different draws and hand ranges to consider, different potential "best" hands for each opponent, more outs to keep track of...

In HE, there are relatively few cards exposed, and there are tracking tools, data bases and software to help players out, but I don't think such programs would help as much with stud, given the hidden cards and bigger boards. On any HE board, it's obvious to a squirrel what the nuts are, and what your outs are. Not so in stud.

I know I'm not yet a good poker player, but I didn't become a winning HE player until I got serious about stud. I think it makes for good general poker mental exercise.