Originally Posted by AlphaC
Midrange boards should
top out at around 90-100 degrees VRM with AVX at 1.35V or so (not small FFTs) with case cooling , peak power output roughly 250W at the wall. AIO Coolers or high end air with 250-300W+ peak TDP potential are required to extract ~200-220W continuous out of CPU because you need to account for thermal resistance of thermal paste + liquid metal (Coffee Lake is not a soldered CPU).
--- OCCT AVX , RM1000i ~ 92% efficient
--- Prime95 AVX large FFT
Both the ROG Hero and Gaming 7 have been shown running 5GHz 1.4V (Aviutl＋x264) with no extra cooling at 90-100 degrees over on livedoor (blog.livedoor.jp/wisteriear/
What you're seeing is largely a VRM heatsink limitation. That's why to fully utilize the potential of Gaming 7 , ROG Apex/Code/Hero, Taichi, Godlike , etc you would need to cool the VRM with a monoblock or better surface area VRM heatsink than the RGB monstrosity on the Gaming 7.
At least one user reported VRM temperature drops on the Gaming 7 from switching thermal pads and torquing down the VRM heatsink more.
With boards such as GBT Gaming 5 (4.1 and 5.3 °C/W thermal resistance junction to case), MSI's M5 (3.8 and 5.3 °C/W thermal resistance mosfet junction to case), Asus Z370-A Onsemi variant (4.1 and 4.9 °C/W junction to case), Asus E/F/G Strix boards (worse for monoblock purposes due to 25A package limit ; 4°C/W thermal resistance junction to case) getting a monoblock won't increase your potential very much since you're mosfet package limited to an extent. You're looking at about 20-30A maximum per phase without adjusting RDS(on) for voltage and temperature (+20-30% difference at between 80 to 100°C). The STRIX E/F/G just happen to have lower max current for the low side fet (25A package limit).
If you're thinking of watercooling a midrange board (not really worthwhile IMO), a GBT Gaming 5 is a far better bet. Firstly, all components for doubling/dual driver are on the front of the board (under the VRM heatsink area). Secondly, it has been shown to run cooler even without watercooling. Thirdly, the mosfets can handle much more current if kept cool (it's the same power design as on Z270X UD5) to the tune of 45A at 25°C mosfet case temperature for the high side 4C10N and 69A for the low side 4c06N.
The MSI M5 and Pro Carbon are decent but you must keep in mind that the dual drivers (up1962) are on the back of the board. The 4C029 has a similar 46A at 25°C mosfet case temp so there's no major advantage in that respect.
The moment there is a VRM block for the Asrock Z370 K6 or Extreme4 , those would be even better than the GBT Gaming 5. The Fairchild variant (dual channel mosfet) can handle 56A at 25°C on the high side channel and 84A at 25°C on the low side. The Sinopower variant can handle 73A at 25°C for the high side channel and 186A for the low side channel. The main reason why you would prefer the Fairchild variant is that it has faster switching times. With the Asrock Z370 K6/ Extreme4 you're more limited by the CPU power connector than the board.
edit: I did the math with the Fairchild and Sinopower on 5 phases in dual driver mode vs the 10 discrete drivers on the Taichi, you'd still come out ahead of a ONsemi/Vishay 8 phase solution using the mosfets on the GBT Gaming 5 / MSI M5 even if they were interleaved. It is partially due to the approximately 2x lower RDS(on) of the low side channel but also due to lower switch times on the high side channel. Of course in reality the STRIX E/F/G, GBT Gaming 5, MSI M5 may not be interleaved.
A stock i7-8700k
draws about 100W in Handbrake with x265 (AVX2) and about 120-130W hammering it in Prime95 with AVX. The i7-8700 is likely going to avoid turboing as high as the i7-8700k for AVX loads.
(refer to ATX12VV power draw http://www.hardware.fr/articles/970-3/overclocking-pratique.html
This thread mainly applies to overclocked, delidded CPUs on AVX or continuous loads with AVX. For your use case, an Asus TUF / Z370-P, Asrock Killer SLI, MSI Tomahawk & lower, or Asrock Pro4 are still not great ideas due to cut down USB gen 2 , features (such as wifi, M.2 slots), and/or audio. The Gigabyte Gaming 3 , K3 , XP SLI & HD3P then become stronger contenders due to Dual BIOS but the MSI SLI PLUS is usually cheaper. The STRIX-H is still terrible since it costs quite a bit for what it is.
If you buy a cheaper board and use it with AVX on stock CPU, the sustained all core turbo will not hit power limits unless LLC is at ridiculous levels.
I would limit your expectations for an ITX board.
For Fatal1ty ITX , you could probably use the Koolance VRM blocks.
Or trim to fit https://modmymods.com/watercool-heatkiller-microsw-x-40-diy.html
I personally wouldn't buy the STRIX-I because even if you put it under water you're limited to about 14.5-20A per 4C86N mosfet (package limit is 20A) x 6 phases means safety is around 150W tops. The Fatal1ty ITX is far more capable due to the 5 phase power design using 60A Intersil smart powerstages along with the heatpiped heatsink.
The way I see it , for monoblocks and VRM blocks you should only buy a board with mosfets that have a higher package current limit
because otherwise you're still limited by the mosfets innate package limits.