Float - Eggbeaters -vs- Speedplay

I am currently using speedplay zeros but I am thinking of swtiching to either frogs or eggbeaters. I initially picked the zeros because:

1. I have bad knees and wanted float
2. they have a low stack height
3. they are light

But now I am looking for a system that will allow me to put on recessed cleat shoes when I want. While the frogs are a possibility, the eggbeaters are up to bat as well. Here are my questions (for people that have used both systems):

1. Is the float on the eggbeaters comparable to that of speedplays?
2. Does changing the stack height really affect power to the pedals?
3. General opinions comparing the frogs to eggbeaters.

Thanks in advance!