Just did some more tests.  Did xbox via s-video again.  Doesn't look so bad from a distance but from 2 foot away it looks pretty messy TBH.  Tested Sky via composite, looks fairly awful but I think that's most down to composite.  Tested DVD player via s-video again.  Initially it looks quite a bit worse than the CRT (outputting to both at once for a direct comparison), but after a while it seemed to become watchable, especially at 4+ foot away.  It was also noticeably sharper than the CRT.  The colour saturation and hue were quite a bit different from the CRT though.
One thing though, it was quite obvious to me that it was a 16:9 image being stretched to fill a 16:10 screen, so everything was a little taller than it should be.
I think Sky via s-video (which I can't test sadly) would be 'good enough', but I doubt it will look 'great'.