Not sure you can actually connect and use three monitors using just the on-board graphics. Download the manual for the monitor and make sure you can do it. Otherwise, no, you won't need a high-end card. Just one that can do AMD Eyefinity or NVidia Surround.
I've never been a fan of OC, primarily because by the time my system is ready for a performance boost, I'm ready to purchase a new system anyway.
-Wolf sends