Like I said, cooling is going to be a major issue that doesn't currently have a solution (as far as I know) Even if it does, you are going to run into the real problem that even if you can cool a 600W CPU, would the average customer WANT to have such power hungry parts? Now imagine the problem in server space where the CPUs are already constrained by power consumption.

The entire reason cloud service providers are looking at and advertising ARM racks is the power savings from operating them.

I think there are almost endless gains to be had on the software side. Current software is so insanely inefficient you could probably triple the speed of the average computer without any hardware upgrade.