I'm struggling to find an ideal video card for my RUBY-9719VG2AR... as I currently have a DP 1.4 capable monitor with proper support for up to 4K with 144Hz.

The board has an odd layout that prevents use of cards that are too long, as longer cards will get in the way of memory slots, so I can only use half length cards that are at most 6.8 inches long.

Unfortunately, most of the cards in the DP 1.4 era are severely crippled when it comes to DOS, with many essential VGA/VESA functions broken or unusable, causing all kinds of graphical glitches, and in extreme cases, games would crash outright due to failed VGA/VESA function calls. The newer the card, the worse the VGA/VESA implementation, and this applies to both AMD and nVidia (the latter being even worse).

Eventually I settled down on a Quadro 2000 (Fermi) which could pass this VESA test and with no major VGA/VESA issues so far, but I'm having another issue... my monitor is too much for this card.

The card would not show anything on system startup. At first I thought it might be a cable issue but I'm able to get a stable output after toggling my monitor's DP version (1.1/1.2/1.4). Switching to any version will enable output, and I can switch it back to 1.4 afterwards and the output will stay working, until I reboot again. Actually, the DP output cannot initially work regardless of my current DP version setting, and a change of DP version to any other one will make it working. Don't know if the problem is due to video BIOS or is just a problem with my monitor. At one point nVidia issued a so-called firmware upgrade for addressing issues with newer DP monitors but that was only for Maxwell and newer cards.

The good part, however, is that with this card, I can use 120Hz with 1080p resolution which is good enough for my use cases with this system... I've confirmed it working on Linux with proprietary drivers (doesn't work with nouveau) but I'm not sure about WinXP. From what I know with some other cards on other systems (mainly Kepler and Maxwell), I simply couldn't use any refresh rate higher than 60Hz. Higher refresh rates, however, work fine with Win7 and onwards.

And here are the questions...

1. Does anyone know a good half-length video card that can do DP 1.4 as well as having a correct (mostly glitch/error free) VGA/VESA BIOS implementation?
2. Is it even possible to "fix" the broken VGA/VESA BIOS codes on newer video cards? I did google about some VGA/VESA BIOS patching but the closest ones I got were about addressing Hackintosh-related issues.
3. I'm not sure about the compatibility between lower DP video cards and higher DP monitors... My monitor can handle DP 1.2 video cards just fine, but this is the first time I tried a DP 1.1 video card and this happened...

EDIT: Tried a bit more... For Quadro 2000, if I use an active DP-HDMI adapter to connect to my monitor's HDMI port I will not get any signal and there's no way to go around unlike pure DP. If I use a DVI to HDMI adapter I can always get signal but capped at 1080p/60Hz (single link), despite the cable claims it supports 1440p or 4K. I don't think a Dual-Link DVI to HDMI adapter exists...

UPDATE: Okay... it seems I was just one BIOS flash away to fix the DP port issue. Flashed a newer, UEFI-capable BIOS version that I got from TechPowerUp, and now I can get working DP output without having to go through all that hassle. But still, it'd be better if there are more recent video cards that could output higher resolution while not crippled when it comes to legacy capabilities...