elitejp (the OP who posted the original thread)
I want to emphasize something someone already posted
Also, the performance increases beyond Sandybridge have been incremental.
http://www.anandtech.com/show/9483/intel-skylake-review-6700k-6600k-ddr4-ddr3-ipc-6th-generation/23
If you get rid of that outlier that's emulation (Haswell got a decent bump for some reason), the difference is, what, 20%? 25%? over Sandybridge. Considering that CPU prices have been increasing quite a bit, whereas Sandybridge can be gotten on the cheap, with an i5 2500k costing around £80 on the ol' Ebay...Nah, go Sandybridge.
That is information from the 6th generation (Skylake review), here is another more recent article from anandtech that compared the top i7s of
2nd generation i7 (2011), Sandybridge
3rd generation i7 (2012), Ivybridge
4th generation i7 (2013), Haswell
5th generation i7 (2015) with ed ram, Broadwell
6th generation i7 (2015) with ddr3 memory, Skylake
6th generation i7 (2015) with ddr4 memory, Skylake
http://www.anandtech.com/show/9483/intel-skylake-review-6700k-6600k-ddr4-ddr3-ipc-6th-generation/9
Depending on the tests there is less than 10% improvement (tests where the cpu is less important and the gpu is the more important thing like gaming), to dramatic increases in performance, 30 to 50% higher speeds and some tests higher than 50%.
Here is anandtech bench where you can compare two processors side by side
http://www.anandtech.com/bench/CPU/39
AMD has not been competitive in the high end even, as an afterthought since Phenom 2. In the middle and high end AMD just flat out disappoints (note Phenom 2 was competitive to Intel's middle end but phenom 2 was 2009 to 2012).
On the low end the best current AMD cpus still are slower than intel i3s in almost all work loads. AMD has been so non competitive that I want to throw out terms (that make cause some people emotions to rise) and these terms are laughable or just sad and depressing. Note I am an AMD fan, but AMD is not the competitive AMD it used to be (due to manufacturing process, and lack of resources money wise and engineers). AMD has been an afterthought for almost 5 years, and has been losing for 9 years and in 3 months that number will be 10 years.
But this may all be different in 6 months or so. Note it can be earlier than 6 months, or later than 6 months, but we are expecting a new architecture from AMD in 2017, a new architecture from the ground up and on a competitive manufacturing process to what Intel is currently doing. How good Zen will be right now is speculation. We also do not know prices since prices in the cpu world are based off performance where you price your silicon to be as competitive in price to performance compared to your competitor by the other company.