I have tried running a 4k desktop with dsr. Performance was same.
I even went and bought a 4k monitor from amazon.
The 4k monitor was a big disappointment.
It was the same size as my 1440 gaming monitor, but underperformed in every single aspect.
I quickly returned it for a full refund.
Good old amazon.
A gaming 1440 monitor is leaps and bounds above an average 4k monitor