Let's first semi-confirm what sort of CPU temps/clock speed behavior are occurring...
Download/install/run both HWMonitor and Prime95/small FFTs...
Note peak core/package temps on small FFTs after 10-15 minutes? As long as cooling keeps you to 80-85C, then CPU overheating would not seem to be an issue...
You might also check to see if any power limit budgets are possibly set in BIOS, possibly limiting your CPU to 90-95W TDP. If you have any overclocks applied at all, and/or MCE enabled (if MCE is enabled, CPU will attempt to turbo all cores to 4.7 GHz (higher if overclocking) under load if power/cooling allow it), you could easily exceed your 90-95 W power budget, and, the BIOS might have protection settings enabled to power down if these limits are exceeded...