As a user of dual monitors, one vertical and one horizontal, I have to admit, there's nothing that makes me happier than full screen Vim on the vertical 23" monitor.
I prefer horizontal mode and 2/3 horizontal splits. For some reason, that works better than vertical splits for me.
xrandr --output eDP1 --mode 1024x768 --rotate 180 \
--output VGA1 --mode 640x480 --right-of eDP1
(From memory, dont paste this to the bank)