Those temps are starting to get on the high end for basically an ideal load. I would recommend running Prime95 Blend test for 2 hours and monitor your temps. I think you'll start to get into unsafe levels. I would recommend an aftermarket HSF like the Cooler Master Hyper 212 Plust to help with those temps.
I'm not sure why your MOBO overclocked itself, but I would check your BIOS and it probably has a "auto overclock" function that is enable, so you can disable it and it should run at normal speeds. Those speeds are safe but not on a stock HSF.