I've fitted the Arctic VGA
Silencer, which claims to operate the GPU at much
lower temperatures than the standard cooler (and
the desk fan's there too). I thought I might
benefit from increasing the voltage to the GPU.

I did try changing the AGP signalling voltage to
1.6V, but that made no difference (I think) and I
can't really see why it should make any, to the
core.

Um. I have an artic on a 9800 pro and can get comforatably up to 430/370 (max is 445/380). Although
variability is a factor in silicon in general, your temps still seem low. Have you got the high and
low fan settings mixed around? I keep mine on high all the time btw. Also might be worth checking
that you are getting good thermal contact.

Upping the voltage makes the card hotter, which is more than likely making the heating problem
worse.

could be that you simply have a card with a hot GPU? I have the same problem with my processor,
XP2800 which simply crashes if the temp goes beyond 60 for more than a second, so any real
overclocking is out. Luck of the draw.

S