I can't believe no one has mentioned that the problem could be that you are running your Macbook Pro in clamshell mode. Having the lid closed traps a lot of heat that would have otherwise dissipated, it's best, even when working on an external monitor to just leave the laptop open.
I appreciate very much your input, but I thought that running in clamshell mode with the latest MBP's was fine? If what you say is true then I have a problem with my current setup....