I had a similar setup, a system I built from tax return money in 2009. I upgraded it in January this year.
The CPU is fine as is and will be fine for a long time still.
1. Upgrade GPU
A single R9 280X or Nvidia 660/760+ will handle the game great at highest settings. A 2nd for Crossfire or SLI is good as well.
2. Upgrade RAM
You can lose the triple channel and go with single or dual channels, your board probably has a max of 4 GB per slot, go with 4 x 4 GB DDR3 1600, totaling 16 GB.
3. Upgrade primary HDD to SSD
For overall system bootup and performance, go with a 256 GB or 512 GB SSD as your C: and keep the HDDs as data drives for storage. Get a 1TB or 2TB HDD to use for backup, Then use REDO backup to save an image of your current C: to the TB drive and restore it to the SSD. A second SSD for the game to run on separate from the OS is even better, You can do that with a 32 GB SSD, but I recommend a 64 GB SSD or 128 GB for room for future expansions and other games too.
4. Preventative Maintenance (every 1 to 3 months)
Make sure to blow out & vacuum dust out of the system, don't overspin the fans with the canned/electric air. And make sure you have a working UPS Battery Backup that the system is plugged into.