XM-L vs XP-G in heat comparison

I have 4 xp-g's in an aluminum enclosure all running at 1.2 A each from the constant current driver. The enclosure gets hot as a potato when touched and the driver is set for the maximum current without having a thermal shutdown, Any current above 1.2 A and it shuts down after a few minutes. That 1.2 A is the threshold value to keep the leds on constantly. Do the XM-L's run cooler at the same drive current ? If so, can I increase the driver current thereby taking advantage of not only the led's efficiency but also a higher current for added lumens and at the same time just be at the driver's threshold before thermal shutdown. Approximately what percentage, roughly , in terms of lumen output will I gain by switching over to the XM-L's.?