I'll try to help you but it will probably take some back and forth messages!
Question: What kind of weather sealing do you need?
If weather sealing is critical then you probably need to go the Nikon way, Canon cameras aren't really sealed until the 1D, the 5dII is a little better but expensive and not fully sealed either.
Warning about Higher ISO capabilities, in most DSLRs the real final native ISO is way below what the manufacturer says and to be honest ISO1600 is probably the native limit for good IQ in most brands.
Question: What about the fps? The Canon 40D is a great value if you need a fast camera, 6,5 fps is hard to match for the price of the 40D. The 50D adds some mpx and other features are they worth the difference to you? You know, not me!
PS: Isn't the G10 15mpx ?
Luigi