There is a thread in the AC forum that covers some of this:

http://www.flyertalk.com/forum/showt...ht=carpet+club

This is a tough call but since you seem to have discounted some of the major benefits of staying with UA MP (upgrades and bonus mileage), then there wouldn't be any problem going with AC.

Mileage reward levels used to be cheaper on UA for some destinations but even there the difference has been narrowing lately.