If you live near a Microcenter, yeah do the combo with the 4670k and the ASRock Extreme4. However, if you don't have that option for example:
Intel Core i5-2500K Quad-Core Processor 3.3 GHz 6 MB Cache LGA 1155 - $180.00 (@ Amazon.com
ASRock Z77 Extreme6 LGA1155 - $167.94 (@ Amazon.com
About $50 over budget, but you get a solid board for the money. It has more features, is SLI capable, but of course has much better VRM's than the Pro3 or Extreme4. Which will be worth it in the long run. Of course the 2500k isn't the newest tech, but it's still a solid chip and is a valid contender to anything in its class (besides compared to what you are using now, it will be a world of difference). Plus, at 4.8GHz which isn't too far off from being possible, it keeps it pretty competitive with Ivy Bridge and Haswell.