the Sync interfaces can help with it, but ultimately it's an issue between
the VGA port on your display and the XRGB2+. The XRGB does output SMTPE timings
(720x480p), while the VGA ports expects VESA timings (640x480p).
I would not go down the Gefen road. It works, but it's unneccessary.
If you buy a new TV anyway, just make sure that the TV has good processing
with component inputs and then use a VGA to COMPONENT transcoder between the
XRGB and the TV. This will fix your problems and not cause any additional lag.
Keep the Extron interface. It will come in handy behind the XRGB.
If you want a solution NOW, get a transcoder and a component to HDMI converter
and chain them up. Both are lagfree and going the component way will ensure
that the full 720x480p resolution of the XRGB is passed on to your display(s).