The newer tires outer diameter is not much larger than the older style. The difference is that there is far less sidewall, so you get less tire side roll in the corners which gives you better handling.
In fact, they are actually lighter as well as a hair taller. I just weighed a stock revo tire/wheel and a stock 2.5 maxx chevron tire/wheel.
2.5 maxx chevron: 10.2oz
revo/3.3 maxx talon: 9.4oz
You actually get almost an ounce less of rotational mass to get rolling. So the little bit of extra diameter may come out in the wash with the weight savings. That's nearly 1/4 pound less rotational mass. Makes a big diff on these little rigs.
Between the weight savings with these tires/wheels and the weight removal out of the trans with the FOC, your removing a lot of rotational mass, so I really doubt you would have needed to drop down your CB at all.