CPU+Mobo for under 300 shipped for gaming with a side of video editing?
Options:
Intel Quad core K series + m/b--able to o/c
AMD Quad core FM2 + m/b--able to o/c
AMD Quad+ core AMD3+ + m/b--able to o/c
Intel fastest CPU in the west, need a higher end m/b to o/c $$$$ (Used $$$)
AMD FM2 (750K, IGP disabled) + either A75 or A85X m/b + faster ram $$-$$$
AMD AMD3+ (6300-8350) + either 970 or 990FX m/b $$-$$$$
Intel combo is more expensive when purchased new but you can buy used cheaper and take your chances with the seller.
AMD FM2 combo is more reliant on faster ram to o/c and is a little more challenging to accomplish but doable. Depending upon which m/b you get an A75 can still o/c and get a lot of features but an A85X is an extremist m/b and is made to oc the cpu and graphics, costs a bit more than an A75 m/b. But a 750k Quad core can be bought for about $80-90.
AMD3+ can go budget and get a six core and a 970 m/b for about half the price of an Intel combo, can easily o/c. Or you can go for broke and get a 8350 and a 990FX m/b be able to be an extreme gamer, this would be closer to the cost of an Intel combo.
It is all a matter of budget and where you are willing to compromise and what you want to accomplish. If you are looking at a system to be up to date and fastest on the block for more than 6 months, you will sorely be disappointed. Though lately Intel seems to be more of incremental step up with their new cpu's rather than revolutionary fast speed demon.
These days unless you are an extreme gamer looking for bragging rights it seems to me that for a mainstreamer most of these new technologies are overkill. Besides with more money left in your budget you can add other stuff to your system, SSD, better case, bigger HD, faster Ram, third party cpu cooler, more case fans, tv tuner card, or have more fun money.
No haters need apply.