I like the RipOffs brand holsters, they use a metal clip that is easy to install on your belt without having to slip the belt through it as you put it on. Both of the holsters I own (one for 6P and one for M6) are fairly well balanced as for how much of the flashlight is above and below the belt line, but I'm not sure how their M3 holster would compare. I can definitely sympathize with the "high holster" problem as I have a few lights that came with holsters that ride up like that, very uncomfortable when getting in and out of the car.
The metal clip design of the RipOffs means it can be installed anywhere you have a horizontal run of something reasonably secure. I hang the M6 holster off the side of my left front pocket, it's down out of the way and does not interfere with getting in and out of the car. I wear jeans and cargos mostly, so that changes things a bit. Not sure if that concept would be comfortable or even work on the more dressy slacks that many LEO's wear.
I think if were faced with the the requirement to carry as much stuff as most LEO's carry on their belt, I would be using a thigh rig to move some of those items out of the way. I think the thigh would be a good place for a flashlight, backup flashlight, spare cells, maybe even the radio. (depending on what type of radio it is, size etc)...
Never know when a routine stop could turn into a foot chase through the woods, I think it would be comforting to have both a good flashlight for you, and one on hand for another officer who ditched his oversized mag 300 yards back
Eric