I cam across this thread trying to figure out compatibility of the x570 Impact with the NCase and I might have some usefult tips and thoughts for you as I have completed a very similar build.
R9 3900x
Asus X570 Strix
Trident Z 3600MHz 2x16GB CL16
EVGA Reference 2080 Ti
Corsair SF750
Cooling:
Apogee Drive II
2x HW Labs Black Ice Nemesis GTX 240
2x Noctua NF-A12x25
2x Noctua NF-A12x15
3x Koolance QDC combo
No Reservoir!
For me the Apogee barely fit. I did not use extender pieces on the but directly screwed in 90 degree fittings. Although the RAM flexing is uncomfortable it still fits my case. I will provide some pictures later.
Another issue is that the AM4 mounting is impacting my VRM cooler. It looks like the CPU contact looks.
You made the right choice going with slimmer tubing. Currntly I am running 16/10mm and while it is fine It is probably severy impacting airflow through the top of the case.
If you still want reasonable access to your systema dn easy exentability I can highly recommend quick disconnects. You will need to make sure that the connecting run for the side rad are long enough to take out the radiator without disconnecting otherwise it wouln't work.
If you end up watercooling your GPU I highly recommend getting a backplate that is comtible with your block (or reuse the stock one if possible). I assume that is a custom PCB so you might no be able to fit a waterblock at all. With the stock PCB the EK block I run only fits properly when I take the decorative element with the branding and 2080 Ti lettering of
I do love the J-Hack cables. Never heard of them before your build but the seem cool. With individually sleeved stock cables I still managed to fite everything pretty much without issue and training is also very much possible I still think you cable solution will be a lot easier and cleaner to handle.
The reason why I consider switching to the impact is that the chipset fan on the Strix is WAAAAAYY to loud. I'd like to run my system as quiet as possible but that results in very low airflow and high interior temps. The Chipset always runs about 30K above ambient at idle resulting in 63C and 3500-4000RPM on the fan- very annoying. I would love to know if the impact suffers from a similar issue, namely how much the delta between ambient and chipset it and what RPM the fan runs at and if it could be controlled.
I am also running a water temeprature sensor to control my fan speed. This reduces sporadic fan behaviour as the deciding factor for cooling is the water temperature. You will need to monitor for component temps when testing but the component will always have a stable delta from your water temperature governed by cooler and thermal interface material. In short loads my fans don't need to spin up but after longer loads the will keep spinning as long as liquid is still heated.
I did not use a reservoir (inside my build that is) because there wasn't enough space for it. I do howerver have an external reservoir I can put into the loop with quick disconnects. Filling and draining without it would be an absolute complete nightmare and I consider this a NECESSITY for anyone building without a permanent reservoir.
I would love some fotos from the front possibly without a GPU installed becasue I would like to know if the DTX form factor prevents running a 240mm bottom rad at the same time.
I am not sure if my choice of a second 30mm thick raditor for the bottom was the best as there is very very little space left between GPU block and rad for air to flow. Initially I wanted to go for an XSPC TX240 and try and fit thicker fans but I don't think it would have been much better. Going slim rad and slim fans would proabbly make for the best quite cooling which was my end goal.
I just want to get this post out and go to bed. I am very sorry it came out so unorganized.
Do you have any particular question? I asked you some and I hope I can help you a bit in exchange.