DavidVioMC :
Thunderballs :
Why are you allowing the size of the case to limit you ?
It is not difficult to rebuild a PC in a different case.
I have tried multiple cases and the motherboard just simply dosen't fit them, and they're just not some cheap cases, they're proper gaming PC cases that supposed to support 99% of motherboards, one of the issues is that 'small form factor' case opens on the right, when PC cases always open up on the left, making the componets impossible to fit since all the ports ect on the back, face inside the case instead of the back like on the small factor case, and Dell OptiPlex 960 will simply not power on if you don't have the heatsink screwed on but when I put it in a different case, I have nowhere to screw on the heatsink since on the small factor case it goes thru motherboard to the case on the another side, I'm not worried about height since I always have my PC side door opened but I'm more censored about length so it can clear the hardrive tray and the heatsink.
Why would you spend the money on a 4K monitor without having a system come close to being able to use it? I'd sell your system, and build one from scratch, I don't see a 235 watt power supply powering a 750 or a 750 Ti without issues. So that means $100 for a video card, another $50 on a power supply, if there is one for your case.
Your friend said you can get a 650 Ti, you have a small form case, did your friend or you actually look to see if a 650 Ti will fit in the case? I'd not waste money on a half-assed solution for a system made to be a basic business or home use computer.