Redraws in gnome-terminal over a network connection are extremely slow.
This is easily produced by using a slow network connection, or enabling a
background image. On a normal desktop, this can also be reproduced by
using opaque window movement and watching the clunky redraw in a
gnome-terminal session. This behaviour appears to be present in all 7.x
versions (probably 6.x too).
They are a bit slower than they should be, because after several days trying to
get them to work correctly in "optimized mode" we just put it in "redraw
everything all the time" mode. The Zvt codebase is indecipherable, we couldn't
fix simple redraw bugs after much effort.
There is no way to fix this without rewriting the Zvt terminal widget. I don't
expect to have time to do that in any interesting timeframe. I would suggest
using xterm for remote display for now. Hopefully someone on the net will get a
chance to fix up Zvt.