I realize your bikes are quite different and am curious what you like about each bike and what determines which bike you will ride that day.QUOTE=RedRockRider;18536915]I don't think the rims are the limiting factor, it is the frame (unless you are trying to put mountain bike tires on, lol).
I just went out in the garage and looked at my 7.9 FX which has 700x35 tires, and there is LOTS of extra space between the tires and frame/fork. I'm pretty sure could easily fit a 700x50 tire with no problem. The fact that our bikes have v-brakes is also huge, as they allow large tires (I have a Giant Rapid 0, and it has caliper brakes, and won't allow much bigger than the 700x28 tires that are on it, unless I wanted to deal with the hassle of deflating my tires to take my wheels on or off (and the front is taken off when I load the bike in the back of my car).
Maybe look into some of the semi-knobby cyclocross tires in 700x38 or so?[/QUOTE]