It definitely sounds like it should work for you. My CPU was running at 4.6ghz after all. That should be a lot more power used even if it's similar voltage, I think?
You could do an experiment with an open case or just board on its box on a table. Then have air blowing directly on the VRM and see if this changes things. You would know for sure it's the VRM temperature and its protection throttling the CPU and not some other strange problem.
When I had this problem I played around with the idea of buying this: http://www.advancetec.co.uk/thermalright-hr-09s-mosfet-heatpipe-cooler-type2.html
But that idea felt stupid as I could have just bought a pricier board in the first place. The shop I bought from was willing to take the board back and let me buy something else even after nearly a month of use so I did that.
Btw... I used whatever BIOS was the most current in February or March this year. The board had a pretty neat ability to go online and search and download the newest file by itself from within the BIOS and that's the BIOS version I used when I had problems with throttling. You might want to try different versions to see if something's fixed.