The motherboard choice for an i5 is good, you can go cheaper though. You should be able to overclock fairly nicely with the current setup.
If heavily overclocking, you may want a different CPU cooler.
RTX is far from a necessary evil in gaming. The 2070s are also not great performers when it comes to RTX and high details. The 1080 Ti still outperforms a base 2080 and only gets beat slightly by a 2080 Super.
https://www.gamersnexus.net/guides/2488-pci-e-3-x8-vs-x16-performance-impact-on-gpus
It looks like performance is impacted slightly. I would think higher GPU loads would be more impacted. Is your motherboard still within warranty?
Funny enough I have the same mouse at near the same DPI settings (I think 1200). Mouse can get pretty artifacty at times. Not sure, but the mouse may be near the end.
Yes, for gaming. I have a 1080 Ti currently. Will be upgrading to 1440p 144hz (current 1080p 144hz). I am really going for the i9 to be more future-proof.
In all fairness, this is X570 vs. Z390 and MPG vs. MEG lines. Asus uses a different VRM design for the X570 boards. I appreciate the input, but I don't believe it scales in this situation.
Sidenote, opinions on the 3900X?