Just a few facts to start with:
My monitor is not 4k, it's just 2560x1440.
I don't play games or do videos, I just process photos.
You can burn a Linux LIVE-CD or create a Linux Live-USB. You would boot off of it and you would NOT install Linux. Ubuntu and Mint Linux both have Live CD/USB you can download and create, as do a lot of other distros. Linux is a world onto itself, so you may want to stick with a MATE version as it is easier to navigate around. If you know XP you won't have too much problem navigating Linux.
OK if the bottom line is that Linux is able to manage 4K where El Capitan can't, so what? Report to Apple the shortcomings of El Capitan?
With my knowledge and experience of Linux, null, and with my luck in that matter (1), null too, it'll take me days or weeks to have it running. Since I am a complete newbie the learning curve will necessarily be extremely steep.
With the time already hogged by the project I am pretty behind schedule with my other activities (well… my life) and so I am struggling to have stuff done and I can't afford spending a significant amount of time.
I think I'd better forget about making my monitor work on my mobo. I'll try to make sure that there is some chance a GPU like GTX 950 will work with my configuration and if so buy one. If the chance is scant I'll have to consider selling away the gear as it is if I can and consider the whole project was a big mistake and a huge waste of time.
If you're not tech savvy building a Hackintosh could be a little overwhelming. But there are other things just as overwhelmng - working with UEFI, getting SSDs to work correctly, installing and setting up Linux, setting up a Kodi box with repositories, setting up wireless access points and securing it correctly, etc. Heck, I curse a lot when navigating around in Windows 10... My next user name is going to be "Alt-F4"...
The building of the hardware was just a breeze. The installation was pretty tricky because I had missed some important points. OTOH, miraculously, the stuff I was worried about like the FireWire card, the CD reader, the LAN connection, etc., were operational at once. It's just trivial stuff that go wrong.
So, for instance the MSI 750Ti Windforce needs two HDMI cables to be connected to the 4K monitor. "Digital: 4096 x 2160 (via 2 HDMI)".
The inexpensive GTX 750s have no DP port and the ones that do are not significantly less expensive than the GTX 950s. My feeling is that it's more or less obsolete.
I would go for a 950 which is significantly more expensive but still affordable, even though it blows up my initial budget. Anyway my monitor has only one HDMI port.
My monitor works perfectly well on my Mini with a mini-DP to DP cable.
Anyway, kiiroaka, thanks for your help.
Nick
1) "If it wasn't for real bad luck I wouldn't have no luck at all." in
Born Under A Bad Sign.