The shop I work for is a production machine shop, the impacts are used for final assembly as well as all sorts of other odd jobs. I feel the 3/8" gets more torque to the socket than the 1/2" with a 3/8" reducer. As I said, the internals are the same up to the anvil according to the schematics. As for performance, I can't speak from experience on the 20v stuff as all my shop runs is 18v. However, in that case they both perform pretty equally and the battery life is very good, probably a half-shift at least. The batteries are expensive, although I think the lithium 20v 3.0 aH batts are a little cheaper than the 18v lithiums through most of our vendors. In any case, I'm sure you wont be disappointed, although personally I'm holding out for a brushless version before I go 20v on an impact. I absolutely agree BTW that the hog ring is far superior for frequent socket changes!!