Gigabyte 970a-UD3P is the best budget board to overclock these CPU's, it has an 8+2 digital power phase and good quality VRM's, good quality board all around, the only thing is the the 970 boards all comes with only one pcie16x slot so if you want to do SLI or crossfire with 2 graphics card you want a 990FX board, these are quite a bit more expensive tho...but the gigabyte 970a-UD3P would defenetly be my choice for a stab at reaching the highest overclocks possible...
The Asus M5A97 EVO R2.0 is a good board too if you can't find the UD3P go with the EVO it has a 6+2 power phase only but will allow for good overclocking too anyway...(make sure its the EVO cause the standard one has only a 4+2 power phase and will not overclock very well and will heats up a lot more)