As an addendum, I’ve done a little bit more testing on the i7 7700k/GTX 1660 TI build. It looks like moving from TAA => FXAA removes the GPU bottleneck. From there the lows seem to be more to do with CPU - I had to drop shadows to medium to maintain a min of 60 FPS. This sort of suggests to me that a 4core/8thread processor isn’t enough for Ultra unit size + ultra shadows, although it might be solved by overclocking the 7700k and using faster memory.
I also tried dropping down to FXAA on the 9700k/GTX1080ti build - this had quite a substantial impact, gave me on average +15 FPS or so. That a much bigger impact than I was expecting, and is in the realms of what it costs me to go from FXAA => 4xAA in Warhammer 2 (c20 FPS).