Well the Malkoff would be the best LED drop-in you could buy. That large brass heat spreader incasing the light helps alleviate the overheating problem, but for good measure I would reccomend the M60L or LL (low and lower versions) just in case. Both are considerable upgrades in runtime, and the M60L really isn't that much dimmer than regular M60, so decide on what you'll be using the light for (runtime vs brightness).
If you want to stick with incandesants, you can get a HO-9 from Lumens Factory and run it on two rechargable 123a cells.
If you don't want to deal with rechargables then the Malkoff is perfect, the Low versions have amazing runtimes and still maintain that great beam. In all proabaility, you'll have little or no heat problems in the G2 if you get one of the Low versions. Heat doesn't even become an issue unless your using the light for more than a few minutes at a time.
Again choose based on what your own personal needs are for the flashlight.