So I'm no math wiz, so please correct me if this is wrong:
If each individual check has less than a 50% chance of success, then increasing complexity does increase the overall chance of failing the challenge, even in the 1:1 system, correct?
I'm in the camp that a balanced skill challenge should be roughly a 50% success rate, for two reasons. 1) The consequences for failure are usually much less than the typical combat encounter. I wouldn't want to get a total party wipe 50% of the time, but pissing off the duke or whatever should be a real possibility. 2) I think that if 50% is the mathematical base for "just usin' yer stats," then a clever party will be able to do slightly better through teamwork, creativity, and circumstance bonus. (OTOH if "just usin' yer stats" is yielding a 7.3% win rate, then yeah, I don't hold out much hope for creativity bumping that up over 50%.)
-- 77IM