Penalizing high hash rates is surely not the correct way.

I'm at 280mhash/s, which is pretty low. Still, I'm sure I'm running less watt-efficient than big miners. I only have 1 GPU working for me, so the motherboard/PSU/CPU/... all eat power only for helping 1 GPU to do some hashes. Those guys with the big mining rigs have multiple GPUs per rig, so they're much more energy-efficient.

And don't forget FPGA/Asic miners. Those have a very low power usage,  but can easily produce more hashes than I do. It'd be unfair to penalize them.

So.. no. Payout should be proportional to hash rate.