With what little I’ve done with normal flippers, I’ve felt like my scuba flippers have been much more powerful (I dive with split-fin flippers). Can anyone give me numbers that compare the effectiveness of scuba flippers to those worn by casual swimmers?

First of all flippers are what seals have. Divers wear fins. And there’s no difference between fins used by scuba divers and those worn by snorkellers or casual swimmers. The only difference will be in how the fins are used. Also some makes of fins are more powerful, particularly the longer ones. I’m not aware of any figures comparing the power of different fins.