The G10 is horrid at 400 or above. The hype is overstated on the 400 performance I think. I certainly coudn't offer anything off it at that speed - grains out.
I am actually considering upgrading to the G11, even though I have only had the 10 for a year, purely for the better ISO performance. Lens is identical. The other features on the G11 don't interest me, the G10 is fine for handling and features. It is just the 400 performance that is so aweful. BUT, before I do swap i need to try a G11 in my waterproof housing first - if it fits and the knobs all work, then I will probably do the change. If it doesn't, I will just have ot put up with it!