I don't know why MR-16 mods aren't more popular around here but if you do up or buy over a 50w MR-16 modded mag (the original MR-16 magmod has to be the Ginseng Polaris), that would make a very nice handheld with a very long-lasting bulb and about 30 mins runtime spewing roughly 1000 lumens as compared to the M6s 500-800 lumens for 20 mins on expensive primary cells.
My 50w magmod :-
http://www.candlepowerforums.com/vb/showpost.php?p=1261322&postcount=1
Using a 3D mag host, powered by a modamag 3D to 12AA batt holder, Osram 50w MR-16 10º spotlight, draws about 4A current. Currently using 2100 mah cells so about 25-30 mins runtime. The latest 2700 mah cells should give me another 5-10 mins.
The bulb is rated for 2000 hrs or more and spews around 1000-1300 lumens (based on DIY litebox).
Of course it is larger than an M6, but I think being rechargeable with a long-lasting bulb makes it a pretty handy light. You can also have the versitility of changing it to other 12v 25-100w bulbs for differing brightness/runtimes, different beam angles and even use LED MR-16s!
I think it's a pretty handy high-powered light with decent runtimes next to my HID. I bought an M6 too, but am not using it in its original form. It's at Milky's waiting for a multi-LED mod. If you really must get the M6, try looking around for one of the rechargeable solutions out there by CPFers.