Refresh rate drop when running additional screen

[PeterScream]

Hi there LTT!  

Recently I've decided to change my screen locations and add an additional one (that would be 5th screen)
Currently running all screens from 1080Ti SC2 Hybrid (awesome card), and I realized too late that additional DVI output is shared with HDMI.
1x 2560x1440 @144 for gaming 
3x 2560x1080 @60 
As it turns out I have 6700K with integrated GPU so thought I'll try to use that puppy to feed that big news screen on the left (pic attached) 1920x1080 @60
Everything works but as soon as I connect that last screen I can see a noticeable refresh rate drop on the main screen 2560x1440 @144.
So, scrolling is not smooth anymore, when typing on the keyboard I can see that the letters appear a bit later on the screen. 
At the same time utilization of the CPU GFX is 24-28% and 1080Ti is around 20-24% - while running all my apps as usual. 
When I disconnect that 5th monitor (from motherboard output) everything comes back to normal. 
 
Question is - is it a windows synchronization, scaling issue? Or anything hardware related. Trying to determine if getting 2nd GPU would fix that issue (more expensive solution). Or External USB GPU for that screen (cheaper solution).
In the future, I plan to upgrade the CPU (to Zen3) so would like to know how much would need to invest to be able to fix this. 
I don't want to end up constantly disconnecting the cable from (let's say 2nd GPU) to be able to play games properly. I usually turn off "extend desktop" when gaming, disabling all other screens and life is good.   
 
I'm assuming it's a CPU GFX sync issue or something of that nature. So getting 2nd GPU would fix that. I never had any experience with 2 GPUs in the system or using an External USB GPU, especially when wanting to have at least one screen running at 144Hz 
 
Full sys spec :
i7 6700K @4Ghz (no OC) KrakenAIO - good temps 
ASUS Z170-E  
32GB RAM(4X8GB) 3600Mhz 
1080Ti SC2 Hybrid
1x M.2
Couple SSDs
1HDD (storage not important) 
EVGA 750W PSU 
 
Screen Config 
1x 2560x1440 @144 for gaming // from GPU (DP)
3x 2560x1080 @60 // from GPU (DP + HDMI)
1x 1920x1080 @60 // From CPU (HDMI)
 
all best, really curious about your thoughts 
piko

[ShadySocks]

You made sure to set the mode of the last screen to 144hz? It might have defaulted to 60hz,

[PeterScream]

Thanks @ShadySocks Its definitely set to 144hz. 

[PeterScream]

Righto so when I went back to bios to disable CPU GFX I noticed that it only had been assigned 32MB mem so that would be a factor. I haven't experimented with that one though as I got 1050Ti on black Friday.

That solved the issue nicely