Questions regarding the G11

I have been using my Canon G9 for quite some time really like it. Although I also have a 20D, 40D and recently purchased the 5DII, I always seem to take the G9 with me on trips. I have the Canon underwater housing for it, and although I had some trouble figuring out the best setup initially, I now think I have it all sorted out. Number one is don't use the built in flash for underwater pictures (too much backscatter will ruin your pictures), and number two is how to control Manual mode by pressing two buttons to simulate the wheel action.

OK so although the G9 is a great camera and it has given me some pretty amazing pictures. I find I can work with the f8 limitation by using the ND filter (probably the most useful and underused item on the camera), however I find that it really is not good at anything over ISO 200 ... actually it is quite bad. And for underwater pictures I really need the flexibility of going ISO 400 or ISO 800 as fish move fast as hell and deeper there is little light, and the dark blue to black is not smooth with high ISO. I am hoping that with the G11 I will get 2 stops better and maybe ISO 800 is possible? Is the ISO 800 on the G11 comparable to the ISO 200 on the G9?

Another option I am looking at is to simply get a housing for my 5DII. The problem is that then it becomes a real PIA to lug all that equipment around. The idea of HD video has me really thinking about it though. I am guessing that ISO 3600 on the 5DII would be pretty close to ISO 200 on the G9?

I would really appreciate any input from people who have tried and compared some the mentioned cameras. Thanks in advance!

I'll go out on a limb and say I'm surprised at some of the high ISO keepers I'vehad with my G11. I regularly shoot 400; hardly ever shoot 800. But that's just me.
My G9? probably 200 max. Others probably shoot faster all the time.

I've had my G11 a couple of weeks, and I would say it has produced about the same or slightly better at ISO800 as my G9 does at ISO200. The G11 also seems to handle white balance better in tricky situations that confused my G9, so I'm seeing much improved performance when compared to my trusty G9. I normally try to keep my G9 at ISO80, but willingly let the G11 go up to ISO800.

Dennis