llkooljo :
Mobo is GIGABYTE 990FXA UD7. I have a Thermaltake Level 10 GT case.
Wow, nicely done. I see that you came to play and not fool around. Now I'm curious what power supply you're running just out of curiosity.
You have an interesting circumstance that not many people are fortunate enough to find themselves with. On one hand, your motherboard is among the flagship-level models that should have the ability to squeeze every bit of performance out of the processor. On the other hand, you have a well designed, quality case that should make it fairly simple to dissipate whatever heat is created while pushing the limits on the overclock. Usually it's pretty easy to point out a weak spot that should be addressed instead of spending the money for the very best air cooler model. In your case, it might actually be justifiable to consider a top-notch unit.
The three best options would be the NH-D14, Thermaltake Frio, or Spire Thermax Eclipse II. Those are the three highest rated air coolers by FrostyTech, who rates them each as being around -4c compared to the Xiagmatek Gaia under 125w thermal load. The question is whether or not you want to spend ~$80+ instead of $20 to net that improvement in cooling. There is a definite possibilty that the Gaia would be more than enough and that you wouldn't actually reach any higher clock speed with better cooling. That said, cooler temps are always better and it certainly would be a nice luxury.
Bottom line, if you are looking for the best, the three units I listed are all fitting. If you are considering the point of diminishing returns, the $20 Xiagmatek Gaia would be truly difficult to imagine actually pegging past the FX8350's heat limits. Can't go wrong either way; it's a matter of preference and resources.