Note that "power" comes from leg muscles. The fins are merely transducers that convert muscle movement to forward propulsion.
In general, the stiffer the fin, especially with high sides (to limit side-to-side movement), the more efficient this transfer and the greater the forward propulsion per flutter kick stroke.
But, it leg muscles are not strong enough to drive the fins, then the stiffness of the fins will promote increased fatigue, cramping, and shorter bottom time.
If using a fin too flexible for the leg muscles, putting power to the fin will simply fold the fin and muscle effort is wasted,
and finally, make sure there is a snug fit between the diver's foot covering and the fin ' cause a loose fit wastes power and may promote fin loss while too snug a fit makes removing the fin in open water a bit problematic. (i.e. I use different sized fins depending on whether I am driving wet or dry)
Bottom line: Its best to match fin to leg muscles. and this is best confirmed by observation and experience 'cause no fin is perfect for all divers in all situations.
For what little its worth, I have used both Power Plana Avanti and Quattro fins in both calm and extreme currents and I am quite pleased with both. I am currently using the Quattro 'cause after 2 decades oi use, my Plana fins have been retired.