To run a membership site, the only CMS i have used is ElevatedX (which used to run HunkMoney, BritishBucks and LatinoBucks) We had a custom install of home-made CMS called 'Kadra' i would stay well away from it.

ElevatedX is ok, except, in all honesty its useful for running many paysites at the same time, and i would say rather overkill for a single membership site.

Carma by TMM is ok, but a little lacking in functionality in todays world.

Stunner has a custom CMS, which is available to our site partners (if anyone is interested in that, give me a shout)