The system I reported on in my previous post does seem to work, but graphical performance is *very* slow.
(xorg 1.8, nv, nvidia Quadro FX 770M)
This problem is obvious for xterm (for the first time in years I had to revert to a native X font to get any speed) and also quite evident in Emacs.
Just displaying 4 audio level bargraph meters (using XPutImage to repaint the part that has changed) raises the CPU usage for X from almost nothing to 85%. To compare, an 8 years old machine also running Arch, xorg 1.7 and nv has no problem at all doing 200 of the same meters, barely reaching 10% CPU usage. As do a number of other machines, all running Arch and using nv or nouveau.
I've read I all could find, tried everything I could imagine, but so far there have not found any solution.
There is something wrong, and it starts with xorg 1.8 refusing to use nouveau - even if this module is loaded X insists on using its own driver. Before I installed nv it used vesa, which failed to use the display at its native resolution.
All of this with the standard install of xorg, and just two files in /etc/X11/xorg.conf.d, one fairly general and the other preventing a Thinkpad's attitide sensors to be seen as a mouse.