Here is a good reference on SkyLake: Wikipedia - Skylake_(microarchitecture). Your systems socket is LGA1156
As you can see your systems socket is not capable to host any of the Skylake CPU's.
Presently Apples best CPU (Skylake) in the iMac series systems is only in the newest iMac: 5K iMac 27" 4.0 GHz i7 (Late 2015). So if you have your heart set on a Skylake system this is the one.
We had thought long and hard last year thinking what would be the best direction for us with our heavy CAD & video processing. Our direction was to jump to the Mac Pro series of systems so far we now have 12 of these beasts and I can tell you they are sweet! Sure newer model systems will come out but so far the Mac Pro is still at the top of the pile (depending on which version you get).