BMX racers can do 2000+ watts and high rpms on platforms... or they used to. They have pretty much all switched to mtb pedals now.

I rode a lot with toe clips, before clipless pedals. I would not go back because of the comfort and safety issues. But with proper cleated shoes and tight straps toe clips have you locked in just as well as clipless pedals, so there would be no performance difference. Just comfort.