I'm running on:
GPU: ASUS Strix GeForce® GTX 1070 Ti 8GB
CPU: Intel Core i7-8700 @3.2GHz
RAM: 16GB XPG Z1 DDR4 3000MHz
SSD: Samsung 860 QVO 1TB SSD
I have to say that from day one I had very little issues with FPS playing on max settings at 1080p. Only really noticeable problem I had was the sieges and for some reason whenever troops AI bugs out. It seems to happen when they're piling up and getting stuck, I'm assuming a pathing problem as lowering the settings had no impact whatsoever (tested A LOT).
I had a couple of little hiccups at huge battles in the field (700+) but nothing that would make me want to lower the settings right away.
By all accounts, Smithers945 you should be able to run the game just as good as me on 4k...there has to be something that's causing this to make you downgrade to medium, even though it's 4k. I wonder if those dynamic shadows are killing it as that's what caused a few lag spikes for me in field battles (weirdly not in sieges, those have entirely different problem.)
I am also running beta and I have noticed some improvements actually, especially on the world map, everything also seems to load faster for me.
Running with around 15 mods at a time.