Twice the rate, obviously... and it all depends on the provider(s).
I've been to AMPs where the providers didn't get along with each other. Always snapping at each other in their native language. Made for uncomfortable session, got a humorous tug after, and sent on my way.
A couple of months later I went to another AMP, and tried a different approach when asking for 4-hands. I planned ahead. I phoned beforehand, and asked if 4-hands was available, and if there was a duo that works well with each other. Booked a couple hours in advanced so they can set it up. And got much better results, including a double-teamed BJ.
Of course YMMV, but the short version is "plan ahead", 4-hands shouldn't be something you can just drop in for, because you'll wind up getting what you get.