I don't think you would see any improvements, as the motherboard doesn't really improve the overall power of your system. What I would suggest is, if you were to upgrade your motherboard - upgrade your CPU at the same time.
It's not worth investing more money into your system, because at the end of the day you're still constrained by your AMD CPU. Yes, it's overclocked, but it doesn't begin to compare with a mid-range Intel Core i5 processor, which you could buy for around $200, and a great motherboard for $100-$150.
This is more than you wanted to spend, I'm sure, but you could sell your current CPU and motherboard to contribute toward your upgrade. Doing this, would give you a huge change in your frame rates, and it would be visible in most games.
From here, the next option I would suggest is buying an SSD - this again will help your system feel much, much smoother. Your GPU is fine and won't need to be upgraded, the same goes for your RAM and PSU.