The suggestion from Marco to try a non-3D DE worked. I tried two methods:
1. minimal CentOS 7 install and xfce install via CLI. Worked fine.
2. Gnome CentOS 7 install and then xfce install via yum groupinstall. Worked fine.

/>/ perfect resolution. Nvidia GT240, driver 331.49.
/>/
/>/ Upgrade to CentOS 7 with nouveau basic driver, all still works fine.
/>/ Resolution poor on wire connected monitor, but perfect on VNC client
/>/ session (1920×1080).
/>/
/>/ Upgrade Nvidia driver via elrepo. 340.58; removed nouveau via
/>/ ‘Software’ manager. Excellent wired monitor resolution.
/>/
/>/ But >> Client VNC connect receives the dreaded ‘oh no, something
/>/ has …..’
/
Are you maybe trying to run Gnome3 through VNC by any chance? Because Gnome3 requires 3D acceleration, and I’m not sure that nvidia driver would simulate 3D stuff in software (nouveau should fall back to mesa in case hardware acceleration fails — typical of a VNC session).

So my suggestion is to try KDE or XFCE or LXDE or Mate or… any other DE which doesn’t require 3D features to work. Such DE should work through VNC using nvidia driver no problem — the only exception is Gnome3.

/>/ Also tried 304 driver (only other one in elrepo for el7) – same
/>/ problem.
/
You don’t want to guess which driver you need. Use the nvidia-detect utility from elrepo, it will tell you which driver to install.

/>/ cannot see any solutions posted as yet.
/>/
/>/ So, what are my options?
/
My choice would be to try a less demanding DE first.

/>/ Catalyst driver will work, but there is a much more active and
/>/ extensive open driver community, which could work better than nouveau?
/
Catalyst driver has always been a pure gamble for me (i.e. worked 50%
of time, supported 50% of video cards, and could be installed on 50%
distributions… or so…). The open-source radeon driver is much better supported.

That said, the radeon community is not any more active or more extensive than the nouveau community. It’s just that AMD has released the specs for their cards, so they have a much easier job of maintaining the radeon driver than the nouveau community (which basically needs to RE
everything from scratch).

HTH, Marko