I have an aging video card in my Mac Pro (GT120) and my trustful Dell 2407WP just died after moving (although I hope to repair it). Looking at newer video cards and getting excited about large (24"+) hiDPI screens (in 2013?), I noticed that most of them list WQXGA 2560x1600 as the maximum supported resolution. I have a hard time believing this is a technical issue given that 1. one can drive 2 monitors of said resolution with a given card (I know there are bandwidth issues but I'm not clear on them) 2. the mobile graphics inside the retina MacBook Pro drive higher resolutions than WQXGA. If I'm buying a card today (say the GTX660) with a supposed max resolution of 2560x1600, what are the chances that it could drive an hypothetical hiDPI display of 3840x2400 (upper limit for Display Port according to wikipedia)? Would it just need new driver? Will this only be possible using thunderbolt/DisplayPort connection and not DVI?
In theory, you can just 'bond' TMDS links together. This is what DVI-dual-link is, basically. The IBM T220/T221 monitors used four of those links to display 3840 × 2400 resolution. Interesting fact: this was back 11 years ago, in 2001.
However, newer display links are not based on TMDS anymore. DisplayPort and Thunderbolt should be able to scale up, but it requires new hardware I assume.
from personal experience:
Manufacturers like AMD list for their FirePro, that they are able to run 2560x1600. I have a 27" 2560x1600 monitor at work.
The FirePro cannot show anything on it, as the monitor has a Dual-DVI-D input, and the connector on the card only has a dual cable for supporting 2 DVI-D monitors. And this is a quite new FirePro.
The 2560 resolution is only reached if all connectors on one port are used. So if you have something with an octo-cable, you can forget it.
On the other hand cheap consumer cards like the nvidia 210 / 610 have a Dual-DVI-output on board. With such a card (and only a single Dual-DVI-D output) one 2560*1600 monitor can be used.
Larger gaming cards can mostly run up to 2 monitors at the resolution. But even some which have 3 DVI outputs have only one or two Dual-DVI-D outputs...
Therefore I would guess that the chances are really low that an even higher resolution will work with actual cards.