If it were me AND I was looking to upgrade components, I'd consider looking for a mobo/cpu combo in the same price range - one that can be upgraded to a bigger/badder CPU. The board will almost certainly come with a CPU that's at least 10% better anyhow.
If it were really me, I'd just wait until I'd normally be upgrading to a newer PC.
Put 'Intel motherboards' or 'AMD motherboards' into the drop-down and sort by price or whatever. Quite a few of those will be < $355 and increase performance by more than 10%, some probably significantly more than 10%.