The LED drop-in that I use in my Mag is the TerraLUX TLE-300; ~600 lumens at the emitter for $70:
http://www.batteryjunction.com/tle-300.html
It's essentially just three LEDs, each with its own optic, all in a self-contained drop-in puck with all the necessary circuitry. It's a minimal difficulty install, you remove the stock Mag reflector and bulb, put the TLE-300 in the socket, done.
Optic lenses mean *serious throw* and the TLE-300 doesn't disappoint, projecting a big fat hotspot with no corona or spill to speak of. You lose the Mag's focusing ability, but when you've got a glaring hotspot that's over two feet across from only ten feet away, you don't need it. The only con is that the hotspot looks a bit like a round, multi-pointed star (the optics to some degree project the square shape of the LEDs) but in normal use, especially outdoors, you don't notice it.
I mainly use my TLE-300 Mag on night walks down our suburb street to the area mailbox. Any time a car drives by going the same direction, it's a perfect side-by-side comparison of light output, and you can't miss it - the Mag is putting out just as much light as the car (the cars don't miss it either, as they usually slow down). It's still impressive every time I see it.
The TLE-300 is my fave Mag drop-in based on its ease of install, use of standard batteries, and good old "damn that's bright"-ness. I've always liked the idea of an LED hotwire/ROP that doesn't require any modding, and this certainly fills the bill.
If $70 is too rich for your blood, there's there TerraLUX TLE-6EX, 150 lumens for $23, which is only about as bright as your stock 6D Mag, but it maintains steady output for over 20 hours. This one keeps the reflector and focusing ability, as it's just a bulb replacement. Not nearly as bright as the TLE-300, but very pragmatic.
http://www.batteryjunction.com/tle-6k2.html
