I'm interested in new rotors.. I got alligator serrated to save weight but i notice heat fade very quickly on steep descents less than a quarter-mile long. They brake noisily but saves 40 grams over roundactagons and stays cleaner. this is a 160mm rotor on a 700c cyclocross wheelset so i'm sure it introduces more torque into the equation than on a 26" mtb due to the larger radius.
the g2 is lighter than the roundagon and the g3 is even lighter than that, prolly give you similar weight savings to those things you have with less noise and heat issues due to increased surface area
however how the heck do you get heat fade on a mech disc brake, their are 3 types of fade from heat (as far as I know): pad fade, you glaze your pads by overheating some of the bonding agents in the pad compound or somthin, you have to sand or replace your pads (so your ride is prolly over didn't sound like what you have) #2 fluid fade which is when you boil your brake fluid, lever goes to the bar and no stopping happens do to gas in the line, but you have mech brakes so... and lastly gas fade, this is somthin that happens on cars i don't think it can happen on a bike but what happens is some of the stuff in the pad vaporizes and you get a gas barrier between the pad and the rotor and the pads "hydroplane" exept on gas. Bike pads are prolly too small and too far from the rotor (cause the rotor isn't floating) for gas to build up, and the slots whould suck any gas out, that is one of the reasons fancy car rotors have slots or are drilled/dimpled.