im still fumbling around with this from time to time.

progress update...

somehow, i have managed to get it happy to have 1600x2560.

[ramble]
that's fine by me (since this is how i've planned to run them anyway). i was about to go splash out on another gfx card or two, n put up with not being able to use my internal hard drives anymore (because they wont fit in that case with basically any card worthwhile card other than the stumpy ones). so, i'm glad i've not /had to/ pull the trigger on that plan.
[/ramble]

i'll try see what's what n not leave things as a mystery here. i dont much like "[magically solved]". better to know what was going on. proverbial blind cats can solve black box puzzles on their own time. ^_^
2 monitors soon (a second stand* enroute), and i'll wanna revisit trying 2560x1600 resolution as well... to be continued.


* angle grinder on the back plate's two fingered gesture was all that was required to enable 90degree vertical mounting on the standard stand (not like they were on warranty or anything). should be ok with the screws, snug fit at the bottom though... pity, i rather wanted the cards n usb sockets at the bottom, rather than acting as dust puddles up top. saves me a day or so labouring making my own mad-max stand for it (which i had made a start on ~ thnx mum(!!) for suggestions that lead me to the anglegrinder solution for vertically mounting 3008wfp).

If that mode is supported it should show up in /var/log/Xorg.0.log. Although nVidia drivers are notoriously bad at giving useful information. Any other hardware that's not nVidia based should give a useful and verbose /var/log/Xorg.0.log information.

Have you tried nvidia-config after you are in X?

Also your bin/cvt output listed 2560x1600_60.00 and you only used 2560x1600 on your newmode line for xrandr. The extra uniquely identifying bit might be important.

If the 1600x2560 mode you got is the resolution you want, xrandr has a --rotate option that might get you where you seek to go.