With that budget you'll want to stick with LGA 1150. I can get you all three of the upgrades you'll want. If you decide to go the LGA 2011-3 route, it is going to limit you to probably 2 of the 3 upgrades (at best) with that budget.
With these upgrades, you'll be able to play pretty much any game at fairly high settings and tackle any task for a good 2-3 years. I tried to get a pretty "future proof" motherboard with some good features:
- Motherboard: MSI ATX DDR3 2600 LGA 1150 [+$110] (Amazon)
- CPU: Intel Core i5-4690K Processor 3.5 GHz LGA 1150 [+$235] (Amazon)
- GPU: EVGA GeForce GTX 960 4GB Super SC ACX 2.0+ [+$250] (Amazon)
Notes: I recommend you get a water cooler for that 4690k. The memory you have may be a bit dated, too. You can upgrade that but it's not necessary. Just be sure to get Corsair DDR3 2400MHz memory. (It's like $10-$20 more than 1600MHz or 1866MHz, you may as well go for it.)