I am adding a second post because I didn't want my comments to get diluted with my technical question above. The 3.5 amp XML is bright as heck and lights up my whole back yard. I am using it with the large Cryos cooling head and a Larue Tactical rail mount. After ten minutes on high with an ambient temp of 85 degF it was warm to the touch but not hot by any means anywhere on the head or body. I am using the copper tape which makes snug contact inside the head. The extra surface area of the LARGER Cryos head works amazing at keeping things cool. This is going to make a great weapon light although since I am running an 2000 mah IMR for reliability, I will only get about 30 minutes on high and 11 hours on low. Side by side with my non scientific eye, low on the 3.5 amp XML looks a little more than half as bright as medium on the 1.4 amp XPG. Something weird I noticed, comparing both on low side by side, the XML looks rosy to me while the XPG looks more yellow. This color difference is not visible in either module on high.
Now for my comments on the XPG. While the hot spot of the XML seems bigger and it is obviously putting out more than double the lumens, I was comparing both lights side by side shining them on a palm tree approx. 100 yards away. To my eye, the XPG is brighter on the tree trunk than the XML, although the XML is lighting up a significantly larger area. The fact that this drop-in (with a 2900 mah battery) will run approx. 2 hours on high, almost 7 hours on medium (30%) and approx. 42 hours on low makes it very appealing to me for a backpacking or walking light, super bright with great runtime.
I have two other XML's in the 5000k which had what appeared to be very natural colors to my eye so I wasn't sure I would like the cooler beam, but they are still very white with none of that "flourescent" look I hate so much. I don't think the green of the trees looks as natural with the 6200k, but it is very subtle and I am very impressed with the sheer lumen output of the cooler color.