Firstly, only threads posted in the wrong section of the forums are moved. The forum is segregated into categories and the tech support category is at the bottom because it is the most convenient location for it as it sits right above the "recent posts" listing that a lot of us use to keep track of what is going on.

The Asrock 970 extreme4 utilizes only a 4+1 phase power design which is a little on the weak side for 8 core FX CPUs, especially if they are overclocked with non stock voltage. This is clearly stated at the very top of the product specification page. Sadly there has not been much in the way of info made available as to what is truly needed for FX 83XX CPUs regarding power so you are far from alone in your frustration. What is happening is that your CPU is throttling down to ultra low clocks for brief periods and thus you see the spike in core utilization, slow cores = more utilization required to achieve the same workload. This most often happens when there is either a thermal event, the VRMs on the motherboard overheating in this case, or the voltage provided to the CPU dropped below thresholds.

The good news is that you are not without options. Before you go out and replace/return the board you can try the following:

Install a decent high CFM (cubic feet per minute of air) fan directed onto your VRM heatsink. If the issue is high temps causing board to suddenly throttle the CPU and drop it's core voltage to bring down temps this should solve the problem. http://www.asrock.com/mb/AMD/970%20Extreme4/?cat=CPU" rel="nofollow - ASRock recommends that all FX 83XX CPUs be utilized with a top down cooler in order to facilitate VRM cooling. 

If that does not help, which I believe it will, then you can try lowering your vcore and essentially undervolt your CPU. This is not ideal as it may mean you lose any overclock you have in favor of stability but most CPUs are able to run at least a little under their "stock" voltage. I only mention this last option in case budget is a concern and you are unable to return the board. Based on the description of your problem however I believe cooling your VRMs will resolve your issue for you.

Good luck and keep us posted.

As a quick and dirty test you can remove a 120mm fan from elsewhere in your case and hold it over the small heatsink between your IO panel and the CPU while running a game, preferably one with an in built benchmark to really put the system through a proper workload. If this resolves the stuttering then find a way to attach the fan there permanently and you should have countless stutter free hours of enjoyment ahead of you. If you have a case with the PSU in the bottom and vents on the top you can try mounting 2 120mm intake fans at the top rather than the usual method of using them as outlet fans. This should be adequate to resolve your stuttering issues.

As for the vcore you should find the info as to how to access it on page 51 of your user manual. Set it to manual and lower the displayed value by 0.05v and then save and reboot. Repeat until your system becomes unstable then add +0.1v to the figure that proved unstable and stress test the system using x264 or prime95 for a few hours to be sure you are completely stable. You should be able to lower the vcore about 0.2v at stock clocks but it will vary widely from one CPU to the next. 

You could also try simply disabling boost and allowing the CPU to run exclusively at its base clock, that will likely also resolve the stuttering. You should be able to find the setting in your user manual. I do not own your board so would have to look it up there myself.

We will get you up and running smoothly, it will just take a little testing and tweaking.

Best of luck to you and please let us know how it turns out for you