Since Haswell-E doesn't have an IGP, the biggest "mainstream" benefit of higher bandwidth isn't applicable. There certainly are benefits to higher bandwidth, particularly for the Haswell-E platform's potential applications, but those aren't my applications. It's not a sin to use Haswell-E if you're not in need of bandwidth -- the "E" platforms are just more capable of solving bandwidth problems.
It seems like most people want DDR4 just for the sake of having a new technology, regardless of its usefulness to them, and are more than happy to fork over "$100" extra for an incremented digit.
There is no confirmation that 16 GB DDR4 will cost $100 more over 16GB of DDR3. The point I was making regarding the additional memory bandwidth - you do
not need high speed DDR4. With even DDR4-2133, the system will have more than enough memory bandwidth even compared to any DDR3-3000 Z97 chipset. The performance gain going above DDR3-2133 on modern Intel CPUs is very small. Therefore, the comment that initial DDR4 memory will be 'slow' is irrelevant for X99.
Even the lowest end X99 board will be stacked compared to almost any Z97 board.
Asrock X99 Extreme 4 comes with Ultra M.2 (so far only available on the Z97 Extreme 6), along with 12-power phases, four PCIe 3.0 x16 slots and 8 DDR4 DIMM slots, Intel GbE Lan. A Z97 board with these features is easily $170. I bet this board will not retail for more than $230, or the $50 premium over Z97, which is not a lot considering it will take 6-core BW-E in 12 months. Add $50-70 premium for DDR4 and say another $70 premium for 5820, and the choice is not so clear cut for many because the CPU+mobo+RAM will be say $170-200 more but in return you get 6 cores+HT.
The -E platform is for people who need >32GB RAM, need 6/12 for very specific applications (not games), and/or who need more PCI lanes for tri/quad GPU. If you fall under any of those categories you know exactly why you're getting that platform. For everyone else, the platform is useless.
If someone is not going to overclock, then of course 4790K is better for gaming than any of the rumoured X99 i7 5xxx CPUs. If you want to use Ultra M.2 PCIe 3.0 x4 and 2 GPUs in SLI, Z97 is also no go for now until say Extreme 9 from Asrock drops -- of course a very niche market right now for M.2 drives and their cost is too high.
But there are already games that run faster on a 6-core CPU. In Watch Dogs, the 6-core beat 4770K, which may or may not represent next wave of games in the next 12-24 months. It's hard to say right now since Watch Dogs is the first such game.
Arma 3 is also very CPU heavy.
There are people running GTX780Ti SLi.
Also, I would wait for 4790K vs. 5820 overclocking results before declaring either a clear winner. If 5820 turns out to be a dud overclocker, and 4790K hits 4.9-5.0ghz regularly, then it's a no brainer for gamers. However, if 4790K exhibits poor temperatures like in the Hexus review, they might only hit 4.6-4.7ghz and say the 5820 can do 4.3-4.4Ghz. The extra 200-300 mhz will not really matter in games but as soon as any game uses more than 4 cores or likes extra cache (a lot of Blizzard games do), the 5820 will walk all over that 4790K. All it takes is just
1 popular multi-player game like BF5.
Again, those not overclocking should pick 4790K.