I'd expect the msrp of an m6lt head to be greater than the m6lt street price. Unfortunately they've always structured their pricing to motivate you to get the whole light instead.
Don't forget about the Malkoff MD60. 500 lumens for 3+ hours is not too shabby. Who knows, maybe Gene will start cranking out 750+ lumen versions soon. I've got a M6 w/MD60 and a M6LT. If I had to pick only one I would take the M6 w/MD60. In the unlikely event the tower fails you can switch back to incan mode in a snap. Plus 900 Surefire lumens is way to bright for most circumstances.