i5-8400 build, need help

Something like this should be a pretty good gaming build for you...

PCPartPicker part list / Price breakdown by merchant

CPU: Intel - Core i5-8400 2.8GHz 6-Core Processor ($187.00 @ B&H)
Motherboard: Gigabyte - Z370 HD3P (rev. 1.0) ATX LGA1151 Motherboard ($143.98 @ Newegg)
Memory: Crucial - Ballistix Sport LT 16GB (2 x 8GB) DDR4-2666 Memory ($138.98 @ Amazon)
Storage: Crucial - MX300 1.1TB M.2-2280 Solid State Drive ($270.88 @ OutletPC)
Case: Corsair - SPEC-01 RED ATX Mid Tower Case ($44.99 @ Newegg)
Power Supply: Corsair - CXM 550W 80+ Bronze Certified Semi-Modular ATX Power Supply ($38.99 @ Newegg)
Total: $824.82
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-10-06 14:31 EDT-0400

> The motherboard you have chosen is fine. It doesnt matter which z370 you choose. Good thing is, it leaves you room for upgrade path should you choose to go with a more powerful chip like 8700k in future.

> Any RAM from 2666 onwards should work fine. Note that Intel do not recommend going below that for on par performance.

> Games still do not use 4 cores mostly. 6 cores is sufficient for the forseeable future and 8 core is like, who knows, 10 yrs down the line maybe.

> Most good quality components have been suggested above.

Edit: You can keep the 970 for now as it should serve you fine for a while.
SSD speeds are pretty fast and going for a faster SSD like 850 evo contributes nothing extra to gaming. Just increases your boot and load times by some tad few seconds, which is not worth the extra price you pay.
And we are talking about something like 10sec vs 13sec.

I think the 8400 is the new king of mainstream gaming. Excellent price point for excellent gaming results. Here are my answers:

1. I would not pair an expensive motherboard with the 8400. Too bad Intel wont release the H or B boards till next year. I have the H170 version of the gigabyte board you selected in my son's PC and I have had no problems at all with it. If you were going to overclock, then it would not be a board I would want, but it will be fine with the 8400.

2. In the past Intel has not had as many issues with RAM compatibility. This is a new platform, so there may be issues that have not been reported, but I have not heard of any compatibility issues as of yet. If you want to be certain, go to the support page on your motherboard web page and it will have a memory compatibility chart.

Intel does not seem to scale as well to RAM speed as Ryzen, so I would not spend a lot on high speed RAM as there are only minimal gains.

3. Nothing is future proof. Quad core CPUs have been mainstream for a decade and games are only now using all the cores. AMD made 6 cores mainstream in 2017, given AAA games take years to develop, there is a high likelihood that by the time games require high core count CPUs, the 8400 will be pretty long in the tooth and be in need of an upgrade.

4. See my build below. The 850 EVO is the most popular SSD in the world, I would go for it. If you have room in your budget, get the 960 EVO as it is faster.

5. I would probably keep your 970 at this point. GPU prices are crazy high due to mining, I would at least wait till prices come back to normal. Volta should come out next year and maybe AMD can continue to improve Vega.

PCPartPicker part list: https://pcpartpicker.com/list/rjrvBP
Price breakdown by merchant: https://pcpartpicker.com/list/rjrvBP/by_merchant/

CPU: Intel - Core i5-8400 2.8GHz 6-Core Processor ($187.00 @ B&H)
Motherboard: Gigabyte - Z370 HD3 (rev. 1.0) ATX LGA1151 Motherboard ($128.98 @ Newegg)
Memory: Crucial - Ballistix Sport LT 16GB (2 x 8GB) DDR4-2666 Memory ($138.98 @ Amazon)
Storage: Samsung - 850 EVO-Series 250GB 2.5" Solid State Drive ($98.94 @ OutletPC)
Power Supply: SeaSonic - S12II 520W 80+ Bronze Certified ATX Power Supply ($39.99 @ SuperBiiz)
Total: $593.89
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-10-06 14:30 EDT-0400

M2 runs hot is a myth unless you have a terrible case with insufficient air flow. Its better to go with m2 for better cable management and aesthetics, but even a SATA disk is fine. Also, as i mentioned before, SSD speeds are already plenty fast and a faster SSD doesnt contribute anything extra. But if money is not an issue and you want more longevity, go with this config...

PCPartPicker part list / Price breakdown by merchant

CPU: Intel - Core i5-8400 2.8GHz 6-Core Processor ($187.00 @ B&H)
Motherboard: Gigabyte - Z370 HD3P (rev. 1.0) ATX LGA1151 Motherboard ($143.98 @ Newegg)
Memory: Crucial - Ballistix Sport LT 16GB (2 x 8GB) DDR4-2666 Memory ($138.98 @ Amazon)
Storage: Samsung - 960 EVO 500GB M.2-2280 Solid State Drive ($233.88 @ OutletPC)
Storage: Western Digital - Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($45.69 @ OutletPC)
Case: NZXT - S340 (Black) ATX Mid Tower Case ($54.99 @ Newegg)
Power Supply: EVGA - SuperNOVA G3 550W 80+ Gold Certified Fully-Modular ATX Power Supply ($79.99 @ Amazon)
Total: $884.51
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-10-06 14:59 EDT-0400

Make a 100gb partition on the NVME drive for OS/Software and keep the rest for your frequently used files like games and movies. Keep the hdd as a backup and storage drive.

The 960 EVO is NVME M2 drive and 5 times faster than any other most other normal SSDs out there... http://www.userbenchmark.com/Faq/What-s-the-difference-between-SATA-PCIe-and-NVMe/105

Maybe 8sec vs 13sec, or something like that. You could go with whichever combination you want. Either should be fine for gaming. I was just conveying all the stats to you.

NVME drives are great and you should get one given your budget. But in the real world, you won't tell much of a difference from a 3D nand sata SSD.

I have a 960 EVO, and my monitor takes longer to boot than my pc.

I would buy an MSI board simply because they have Enhanced Turbo which allows all cores to run at maximum turbo speed.

That is for unlocked(k) processors. Not the locked ones. The locked ones have a fixed all core turbo.

Alright thanks.

NCIX Tech Tips did a comparison of gaming level load times comparing SSD to M.2; times were identical. Not one second saved.

But 5 second boot times, and the 4 min Windows install time, and near instantaneous opening of docs, etc, are nice! ( but for purely gaming , that extra $100 for a 500 GB drive would be better spent on a better GPU, IMO...

I can't tell a difference in game load times from my 960 EVO and 850 EVO. Virus scans are very fast for both of them. Boot times are faster with the 960, but we are talking about the difference between a few seconds.

The nice thing for M.2 is cable management. M.2 are very clean.

I would probabaly save the $100 and just get the 8600k. But I like to overclock. The 8400 is really nice though and is an excellent gaming chip for the price.

I'd save the 100 and start thing about a GPU when Volta comes out and GPU prices become reasonable again.