Got my card yesterday after paying the relevant customs duty.
No problems removing old 7800 or installing the new card, made the minor adjustment to the plastic casing and the card fit very nicely.
Installed 169.04 drivers and then benchm'd using 3dMark2005, and I got just over 8000 3dmarks. A good improvement from 5600 from the 7800.
I've then flashed the BIOS to 600/700 as a starting point and am now getting 8880ish points in 3dMark2005 (I know it's not a realworld test, but it gives me comparable results from overclocking)
As I've got a 1680x1050 22" monitor which I run my laptop display through, I'm hopefully going to see good results from running games at that resolution, something the old 7800 struggled with, and as we all know, running games at less than native res on a LCD can be a mixed experience.
Thanks for help and advice, I'm probably gonna stick to the 600/700 clocks for a while unless people think there really is loads more there, but from what I've seen I won't get much more out of the card.