I have the Asus M5A97 R2.0 motherboard myself with an FX-6350. I can overclock my CPU to 4.5 GHZ on stock voltages just by raising the multiplier, and it works great for me. However, it is a 970 chipset board, but the R2.0 version does feature pretty good VRM heatsinks, and if you have a decent CPU cooler and case with good airflow, you could probably reach 4.5 GHz with some tweaking. It's pretty hard to find a decent 990FX chipset board for $100 or less, however I saw a good cheap Gigabyte one for around $140. If that is too much though, the M5A97 R2.0 or the EVO version are both pretty good options that I trust from personal experience.