Considering the past problems with MSI motherboard VRM's I'd say you are lucky all it's doing is throttling. They have been known to burst into flames in the past. If you only have the budget to upgrade one part it needs to be the motherboard. Maybe you can sell the MSI afterwards to get enough to upgrade the psu or at least start a new PSU fund. I am not bashing MSI, just that their AMD motherboards have been known to be sub-par.
“Physics is like sex: sure, it may give some practical results, but that's not why we do it.”
Motherboard VRM's overheating would be my guess too. Stock settings should not reach 60c either. I imagine you are in high ambient temps as well. Need improved cooling. Try setting a fan directly above the VRM's and retest.
ALSO- make sure you do not run Prime95,IBT or LinX to stress test.You could have a fire. MSI also states this.The problem is not the throttling,the problem is the overheating.In this case throttling is your friend.