Just curious after looking at the back of my SK-68 if anyone has tried modding it to run different batteries. It looks like there's a fair amount of aluminum that could be drilled away without modifying the threads for the tail cap. I was just thinking since I use primaries for batteries, it might be able to fit a CR123A (plus a spacer to make the electrical connection). This would give it the power of the 14500 but with a primary battery instead.
CR123's don't give the power of a Li Ion. There are lights very similar to the SK68 that are setup for CR123 if that's what you desire. It wouldn't be worth modding unless you just wanted something unique.
I was thinking more for light output. I've heard a lot of people say how much better the SK-68 looks with 14500 and thought maybe it would perform decent with a CR123A compared to a AA. I haven't searched for a "zoom" light running CR123A, but I would guess they exist too.
I have used the Lithium primary CR123's, and compared to the 18350 cells I have, there is no comparison. The Li Ion's really are they way to go in any high amp flashlight. Also I remember when i was flashlight shopping a while back, it was actually easier to find zoomie CR123 lights than it was AA's Check out DX or any of the China sites that will sort by battery size, there's quite a few of them out there. My personal opinion is that if you decide to upgrade from the more basic AAs, just spend your time learning about and purchasing Lithium rechargeable batts, you won't regret it.