I know what the differences are between the Haswell and Devils Canyon. Too small to justify upgrading from the 4770k to 4790k and as i said, would have been better to wait. As for the Z87 vs Z97, the biggest difference would be in future proofing as the Z97 has support for the 5th Gen and beyond CPUs. It also has support for SATA express ( more through put for SSDs ) as well M.2. Incidently, I am not dissing the 4770k. It is a very good CPU and I have the one in here clocking 4.5. These days, the way things are designed, you are primarily using the GPU, and in the case of the newer Nvidia GPUs, they will also take over some of the computing duties as well. That comes down to the Bandwidth and your PCIe lanes. The MOBOs for the Skylake witth supposedly feature PCIe 4.0. The Intel Extreme boards ( x99 ) already feature that. I had my i7 2600k on a Z68 MOBO. Fine, at the time, then along came the Z77. I was intially running a GTX 560Ti then went to a GTX 680. Would have been better of having the Z77 with those cards. The Z68 was PCIe x16 2.0 and the Z77 was PCIe x16 3.0. Wider lanes are always better. The bottom line is, if there is a newer chipset available, go for it.
I don't want to get too bogged down with this and offtrack, but there's a bit of mis-information here.
- Broadwell will run fine on Z87 motherboards as long as the manufacturer provides a BIOS update. In any case, Broadwell offers very little for desktop enthusiasts.
- PCIe 4.0 is not out yet and all the leaked Z170 boards (for Skylake) do not feature PCIe 4 (nor does X99)
- PCIe bandwidth is very, very rarely a bottleneck for gaming graphics cards. Even PCIe 2.0 x8 is enough is almost any situation. A single card on PCIe 2.0 x16 is still absolutely fine.
- We've yet to see any serious SATA express SSDs on the market, M.2 looks more likely but you can always put that in a PCIe card.
I agree with your final statement, that new chipsets are "better", but in reality the gains are usually very small. There are heaps of happy enthusiasts still sitting on Z68 mobos with 2500k or 2600k processors that are basically offering the same gaming experience as a high end Intel build 4 years later. Graphics cards are still improving, but in reality progress in CPU has slowed to a crawl and unless you really care about newer features, there's not much pushing people to upgrade.