Size, output, runtime : pick two that you want and the third goes the wrong way.
Example. Small size and high output means short runtime. Long runtime and high output means big size. Small size and long runtime means small output.
There are many lights that can put out more light than a Pelican M6. If you need more light and more runtime, you'll pretty much have to go up in size.
By more light, do mean more throw or more total lumen output? Do you need a tight spot light to reach out far, or do you need a bright medium range flood of light?
Are you totally unsupported with this light (belt or pack carry), or are you near a support vehicle? A rechargable with a spare battery pack and an in-vehicle charger (or just an inexpensive inverter to plug the charger wall-wart into would work) might be the way to go.
Incan or LED? An EL Hyper-Blaster runs for what, 8 hours on high off of 2 D cells. An EL Blaster3P runs on high (to 50% output) for 24 hours off of 3 D cells. An EL Tri-Star Phazer runs 8 hours off of 4 C cells. A Surefire L2 2x123 on high (100 lumens) puts out more lumens than a PM6, but is more of a medium flood than the PM6 tighter spot. On low (15 lumens), the L2 runs for 18 hours. A Surefire L7 LED rechargable gives you 2+ hours of 75 lumen light, then swap battery packs. A Pila G3-series lets you run off of 2xLi-ion rechargables OR 3x123 with 130 lumens (rated) output for 50 minutes (incan) or you can run the 5 lumen tailcap for 60 hours. Or you can have a half dozen PT40 (not a good light for LEO prime light, but they are decent inexpensive lights with pretty good output and a usually pretty good beam) loaded with 4xAA lithiums and just grab a new light when the one in use dims.
There are many choices, you have to decide what you want and what you need.
