I see two paths to upgrading here. The cheapest is to replace your CPU with a Xeon 1230 V2 (make sure to get the V2 which is LGA 1155)
https://pcpartpicker.com/product/DKFPxr/intel-cpu-cm8063701098101
https://www.cpubenchmark.net/compare.php?cmp%5B%5D=1189&cmp%5B%5D=1191&cmp%5B%5D=804
To get a more significant upgrade you have to replace the CPU, mobo and RAM. The new i7-7700K approaches the performance of a i7-6850X
https://www.pugetsystems.com/labs/articles/Premiere-Pro-2017-Intel-Core-i7-7700K-i5-7600K-Performance-884/
Here is a partial system build keeping your PSU and GPU. I did not add storage, it is a consideration too.
PCPartPicker part list:
https://pcpartpicker.com/list/wkLfD8
Price breakdown by merchant: https://pcpartpicker.com/list/wkLfD8/by_merchant/
CPU: Intel Core i7-7700K 4.2GHz Quad-Core Processor ($344.75 @ OutletPC)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($27.88 @ OutletPC)
Motherboard: ASRock Fatal1ty Z270 Gaming K4 ATX LGA1151 Motherboard ($139.99 @ SuperBiiz)
Memory: Corsair Vengeance LPX 32GB (2 x 16GB) DDR4-3000 Memory ($207.86 @ NCIX US)
Video Card: XFX Radeon RX 480 8GB GTR Video Card ($0.00)
Power Supply: SeaSonic M12II 750W 80+ Bronze Certified Semi-Modular ATX Power Supply ($0.00)
Total: $720.48
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-01-24 08:01 EST-0500
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