Yep. 6/4 is much tougher, also more costly and more difficult to machine. Also much worse for heat conduction. But really, it's just more costly to produce.
I also prefer 6/4 but it would definitely increase the cost.
Yep. For creeping around at home, AA provides better low modes. For poking around outside, 14500 gives a lot more punch. Both cells provide the same moonlight mode though, which is cool. It may also explain the use of pwm on high mode, but this is only a theory.