Your best purchase is an SSD. Bar none. 240GB SSDs have dropped to near $100 ! 120GB at $60-$70. With Win8 you will be booting in less than 10 seconds, and it simply takes 'snappy' to a whole new level as far as opening apps and general navigation.
I've got a GA-990FXA-UD3. It's a great board, but unless you need x16/x16 or dual-eSATA it's over-kill. The GA-970A-UD3P will work just dandy with a single discreet card, and the electricals are the same as the GA-990FXA-UD3. The -UD5s & -UD7s upgrade to more fancy electricals.
The FX-8320 is a great bargain at $140 -- otherwise, the FX-6300 around $110 is the ticket.
In a gaming build, it's your video card. The R9 290 is simply killer at it's current price point --- the R9 280X, too.