As long as you are using dx11legacy it's going to be fine, but definitely get the 2080ti for the extra VRAM. You can get 60/30 fps in 5-box easily and good performance in 8-10 box if you have the patience to find the right settings. I found slot swap made a lot of difference, especially switching off any anti-aliasing, low settings for shadows and water. For CPU usage you could maybe try lowering the view distance / ground clutter / etc. But really 90% CPU is no problem as long as you have sufficient cooling. (I have similar to you 4k screen, 2080ti, i7-8700K and 32gb ram).
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