I'm clueless about a VT1300, have only a VXT1200 at home. The VXT1200
looks as if it is a stripped VAXstation.
The box is fairly similar to a VAXstation 4000 VLC and the way it
boots looks familiar. I'm sure its firmware, given the
price per MB in those days, only supports the hardware DEC put in it
at the factory. I think the VXT1300 has the same
limitations. With the available hardware I think you're stuck,
performance wise. A way out may be running an X server on
another platform, say a pc with linux. If you want to stay on VAX
hardware then you might try to find yourself a
VAXstation 4000 model 60, 90(A) or 96. Even the -60 outperforms the
3100 and a -90A will impress you: it's twice as fast
as a VAX 4000-100.
Hans