M380 vs M390 in terms of lag?

[johannnn]

Thinking of getting 27" 5K (256GB SSD obviously).
Is there much benefits of getting the M390?
I dont game, dont do video editing. But I hate UI lag, and I assume 5K pixels is quite tough to handle for a GPU.

 

[Lunder89]

In terms of UI lagging, there will be no difference between the two.
The UI lag isn't really a problem of enough present power, but more some bad coding on Apples part.