Sandy Bridge (2500K) to Skylake (6600K)

You'll see a fairly small jump with gaming but still worth it for newer motherboard features (USB3, multiple PCI-E ports, etc), but with things like Office, video encoding, and other programs you'll see a noticeable increase in performance.

Problem is, DDR4 ram is expensive right now.
 
Oh? Z170 platform will use DDR4? haven't follow much cpu news since things start slowing down after Sandy Bridge. Not going to upgrade soon BTW. just asking for opinion about it. Personally I'm interested what Zen will bring as well but though I 'm not expecting big things with it.