Not sure why you are comparing the 980 to 970 series here.
The 980 “non-pro” has the same endurance/reliability as the pro version.
Either are already plenty fast (comparing two models of Ferrari here…), the “pro” will be marginally faster on brief occasions and only if properly cooled, otherwise it heats-up and throttles quickly. The non-pro is a bit easier to cool and quite less expensive (esp. so when you buy 2). If the near $200 gap (2 units +tx) is non-material to you, just go for it! But only if you provide proper cooling, otherwise it’s a waste.
Good info on the H100 cooler.
It shows that liquid cooling is not always a panacea to have a quiet machine.
It’s usually targeting gamer machines more than quiet/studio machines, so make sure you inform your PC builder of your priorities and they should be able to help making the right choices. I would definitely agree a well-built air-cooling can be better/quieter than a poorly selected liquid-cooling solution! RGB lights don’t make things quieter
And yes, having the ability to force a fixed fan speed can be valuable to reduce the perceived noise.
It all starts with generating less heat, so scaling down the GPU to only what you need is a good practice. The Quadro 620 is probably still 2x more power than needed, bust just make sure you have all the monitor connections you need. Using a recent model as someone suggested is also important. Personal note: the GPU fan is presently the noisiest part of my setup.
The Corsair PSU they offer is not the most quiet, but still a good pick. I would spend my money on an HX850 (or SF750) for silent operation under moderate load. (use the $$ you saved on the SSD )
Regarding CPU now. Both 5900X or 5950X are good picks again, but the 5950 will run a hair cooler in theory (lower watt per core ratio). If money is no object, go for the 5950, but you won’t regret using the 5900 either.
Boy… that post is already too long…
In summary, this PC vendor seems to be credible and use good components, but oriented more on gamer machines than silent PCs. Get someone on the phone to talk about your ‘silence’ preferences to see how they react and if they can make recommendations in that direction.