As 54regcab said ECMs can be adjusted to several HP, adjust the PSCs to the highest rated ECMs HP and you should be fine with air delivery. I would recommend ECMs if cost isn't an issue because when there isn't peak loads, they can say some energy.
I've changed a few that were rated at 1 HP. And the amps were rated at around 6. I didn't see the need to go that high for a residential unit. The biggest I've ever replaced it with is a 3/4 PSC rated at 4 amps. I've had no problems to date. If I ever come accross one with a very big blower wheel then I would consider going higer than 3/4.