The FX Series has allot of potential for those that like to tweak their OC ....... Their big drawback has been their power consumption requiring one of the better Motherboards to handle the power draw and big cooling to handle the heat generated. Simply put the more you try to OC your FX Chip the more expensive it will get. Most boards can OC to 4.3 / 4.4 GHZ if you have adequate cooling but to really put the screws to the chip and get those big numbers you need to spend some big bucks on cooling. Yes Kenrou there are a few exceptions out there but they are just that .... exceptions. Here is a thread I did when FX first came out on what exactly I went through trying to cool an FX8150 to 5GHZ ......
http://www.overclockers.com/forums/showthread.php/715371-Build-FX-Tamer-Water-Cooled-Upgrade
You don't need to spend big to OC ..... here's another example of 4.7 Gig on a budget ..... but you won't get much beyond this without some bigger upgrades in cooling and most likely motherboard.
http://www.overclockers.com/forums/showthread.php/741239-FX-8-Core-with-Gigabyte-GA-990FXA-UD3(REV4)
There are plenty of examples of builds out there to look for we had allot of people come in over the last 5 years or so looking for help with their rigs OC ...... they all came down to heat / poor cooling or poor choice of a motherboard. If you decide to get an FX system take your time, figure out your expectations first and do it right the first time. I'm a good example of this ..... I had roughly $1000 Canadian in my cooling (that includes shipping and duty charges) to run 5.1GHZ 24/7 on my FX8370 with max temps on Prime 6hours + of mid 50*C ....... I would have to go look though backup drives to find my old results and frankly I have too much to do right now for that.
Good luck UT if you decide to do an FX build ..... ask some questions there as there are more then a few guys here that will help.