CPU overload related with 4K monitors ?

Computer) I7-7700, 16gb ram, GTX 1060, / Win 10 64bit

Interface)  SPARTAN A + 2 master keyboards are connected

Track) I normally used about 10 midi tracks + 10 audio tracks for one songs

I have some questions about CPU overload problems of StudioOne4.

I used CUBASE before, however i got CPU overload when i worked at 4K UHD.

I heard reason of this problem was because 'CUBASE takes memory not from graphic-cards , from CPU'.

and lately I changed my sequencer from CUBASE to Studio One to solve this problem.

But, unfortunately, I got same problem at Studio one. (got CPU overload/jumping too high at 4K UHD)

I downgraded my graphic-resolution from 4K to FHD (1920x1080) to test, and CPU usage went down; however it still too much high even I used only 3~5 MIDI tracks !

Actually my computer never got any CPU overload before when I used over 15~20 tracks at CUBASE (under FHD resolution, as same above).

I just wanna know why this happening and solutions for this.

So here the questions)

1. Is Studio One takes graphic memory from CPU not graphic cards , just same as CUBASE does?

1-2. If it does, is there any solution for this? (actually I really want to work at 4K monitors)

2. Or is it just matter of my poor audio-interface? (should i upgrade it now?)

3. Is there any another solutions for stabilize CPU usage ? (setting or checking some menu in the program-)