So in other words, you don't know if you'd be able to push a set of doubles and multiple stage bottles with Force Fins....
actually yes, in fact I do know that I can push all that around, since I used to work as a Navy Diver, pushing doubles, tools, lights, cameras, and even pnuematic tools once in a while. all with absolutely no issues what so ever. And having to move about 300+ foot long ships and avoiding seawater intakes. I don't consider any of that technical diving, as I did it Air and all within no-d limits.
and if my testimonial and the below threads aren't enough for you, watch some of the DeepSea detectives with John Chatterton, who normally wears a pair of the Excellerating ForceFins, if a venerable wreck explorer like this wears them, there must be a reason.
here are a couple of other threads with testimonials from other divers including Blair Mott from the Jean-Michel Cousteau Ocean Futures Society Team (who as I understand it, exclusively use forcefins).
http://www.scubaboard.com/forums/force-fin/209923-explore-your-own-backyard.html
http://www.scubaboard.com/forums/force-fin/213028-they-still-look-different.html
http://www.scubaboard.com/forums/force-fin/212212-force-fins-12-04-07-a.html
as for which fins I use- well I currently have a set of Extra Force Tan Deltas with Whiskers and a pair of Military SD-1. I used to have a set of Pro's but a friend of mine "borrowed" them about 3-4 years ago and I haven't seen them since, except while we are out diving. The Extra Force TanDeltas are absolutely fantastic fins and accomplished every task with ease. If you really enjoy the frog kick then the Excellerating ForceFin is probably a better fin, as it was designed to maximize thrust from a short snappy kick, just don't read this as them being a one hit wonder, because they do it all
As for the SD-1 Military's well I only have about a dozen dives on them right now, but I really like them. They are not as powerful as the Xtras, but much more manueverable and easier to kick. They proved themselves on the 2nd open water dive I did with them. I was off OBX, NC diving on the Proteus. Well the point is, there was a roughly 2 knot current on the down line and of course I let go of the line (had to rearrange some gear that came loose on the entry, yes I know this was really dumb) and when I looked up realized that I was probably 100ft downcurrent of the downline. Well, I just decided that I will kick my way back to the line (I could see the bottom and the boat so I wasn't too worried). Well the next thing I know I am back at the line. As I grab the line something dawned on me, I wasn't out of breath, I wasn't even breathing hard, legs felt fresh, and I ask myself, "how did I get here?" Then I realized, man these fins rock!!