I've recently got the M60L and the regular M60. Took them out for a walk last night, along w/ my SF G3 and found some interesting things... The M60 is insanely bright at short to medium range. It just lights up everything around you at close to eye-hurting brightness. It's definitely as bright as the P90 in my G3, and I think a good bit brighter really. M60L is clearly not as bright, but not by a whole lot, ie it's in the ballpark.
What's interesting is that at a distance the M60L will light everything that the M60 will, just a little dimmer. And at the same distance, the brightness of the M60 doesn't make up for the fact that it's LED and a broad beam, and thus you can't make out any more detail than you can w/ the M60L. At that distance, the incan p90 really wins (granted, it has an extra battery).
The beam on both the M60 and the M60L is very useful without the sharp drop to blackness at the edge that I find distracting for outdoor use.
So, if I had to pick one of the drop-ins for sheer usefulness, I'd take the M60L as the gains in runtime are greater than the loss in brightness to my eyes. And, it lights things up w/o blinding me. That said, I think for the time being I'll keep both as the sheer insanity of the M60 is fun to play around with. Can't think of a lot of real life situations where it would really be more usefull than the M60L though. (I'm not a gun/tactical guy).
Concisely, based on a limited evaluation, at short to medium range, the M60L is bright enough, and at long range the extra brightness of the M60 doesn't get you a whole lot of extra detail.
Hope this makes sense and is of interest. I'll update as I play around w/ them more...