If I was going with a 4090, I'd pair it with nothing less than a G-Sync Ultimate monitor. Definitely NOT a G-sync Compatible anything.
Check here, sort by Ultimate and you can see by size and refresh rate. It's not about the highest refresh rate either, they'll all go high enough. With sim's is more about the lowest. 
https://www.nvidia.com/en-us/geforce/products/g-sync-monitors/specs/

Edited July 3, 20232 yr by Dave_YVR

How about this?

https://www.ebuyer.com/1264422-asus-rog-strix-xg27uqr-27-4k-144hz-1ms-ips-gaming-monitor-xg27uqr?utm_term=&utm_campaign=PLAs||Computer||Monitors||Med&utm_source=adwords&utm_medium=ppc&hsa_acc=4863007528&hsa_cam=10757315445&hsa_grp=107778867484&hsa_ad=454405973955&hsa_src=g&hsa_tgt=aud-943673651254:pla-1634589644762&hsa_kw=&hsa_mt=&hsa_net=adwords&hsa_ver=3&gclid=CjwKCAjw44mlBhAQEiwAqP3eVtdGwYgCOs2UHqfRdfDBGFF0m_gSjnbrdRo60QsxAIdF9JkPXMxmChoCoDAQAvD_BwE

However.....it doesn't appear this monitor supports HDMI 2.1, and my research shows HDMI 2.0 can only output 4k/60HZ so why is this monitor advertised as 144hz - I'm so confused?

EDIT:  On further inspection this monitor is Display Port 1.4 compatible which if my research is correct allows 4k/144hz!!?  And is GSYNC compatible AND fits my budget!  I think I might have found a monitor!  Can anyone disagree?

Edited July 4, 20232 yr by sidfadc

17 hours ago, sidfadc said:

Can anyone disagree?

 Sorry for the late reply, 10 hour shift at work today.
My personal gripes with this one in particular would be

1 : it's size, 27' is really quite small these days and with 4k you really do want something bigger. With a 27 you could still easily use 1440 and probably not even notice a difference except in your frame rates.

2 : It's only G-sync compatible, with a supported refresh rate is 60-144Hz. Meaning that it doesn't have a G-Sync chip in it, so it's more of a fake G-Sync and won't sync the frames below 60fps. Ideally you want something that supports down to 1hz.  Sure even with a 4090 you may never encounter less than 60fps, but you probably will at some point and WHEN you do, you will know it instantly. I don't think I would ever game/sim with anything else ever again. 

Edited July 5, 20232 yr by Dave_YVR