Originally Posted by
Kagthul
I'm seeing two options for you.
Option 1:
Upgrade the current rig.
You're looking at more RAM (another 8GB, about ~50$ for DDR3-1600)
An aftermarket CPU cooler (Honestly, a 30$ Coolermaster Hyper 212 Evo will do you fine)
a new GPU
(possibly) an SSD.
Benefit: Less cost. (MUCH less cost). Performance will be... pretty good. The performance difference between the current i5 6600K and y our 2500K isn't so big as to be huge.
Downside: this is pretty much it for this rig. There's no upgrade path in the future. If you have the money to spend now on a 1000$ new rig, but might not have that money available when it comes time to upgrade next, it might be worth rebuilding. I know how my budgets are, and sometimes i have the money now but if i wait till later ill have to use it for something else or it wont be available.
Option 2:
Build new (re-using a few old parts).
You can probably keep your old case (if you want), old media drive (DVD/RW), and old HDD for Mass Storage if you want to use an SSD.
Your PSU is probably high enough wattage, but after a certain age... i'd say its worth getting a new one.
Youll be looking at a new CPU, RAM, Motherboard, GPU, PSU, and maybe SSD.
Will definitely be more expensive, but...
Benefit: An entirely new system for the most part that still has 2-3 1/2 years of upgrades in the pipeline (Socket 1151 is here to stay for the remainder of Skylake, Kaby Lake (late this year) and Canon Lake (late next year). If you decide you want to upgrade later, you wont have to scrap the whole system, you can just upgrade one part.
Downside: Obviously more expensive.