Hello Kodiakk,
I'd recommend the Zebralight H600 MK II as well. Because of the awesome output, runtimes, size, & weight, it's my all time favorite headlight for hiking, camping, hunting, fishing, and running at night. I spent the last several years looking for this headlamp, and believe it to be the best around for my uses.
I live in Georgia though where it is decently warm, and have had good results with my Li-ion 18650 batteries, even in colder conditions (close to 0 degrees fahrenheit a few times)....but I have never used it in extreme cold such as found in Alaska. You said in your original post that you have used 18650 in your Klaurus up there. Sounds like you are on that island during the warmer months, but Have your 18650 Li-ion batteries performed well in the extreme cold...if you've ever used them in the extreme cold?
If the answer is no, then I'd recommend sticking with headlights that use lithium primary batteries such as the AA Lithiums made by energizer or the lithium CR123 batteries that you can use in your Klarus. "Primary" batteries are just single-use batteries & are not rechargeable. They perform exceptionally well in extreme cold conditions, and have the best runtimes of any of the other batteries available. If you need to go the route of lithium primary batteries then I'd recommend the Zebralight H52 (which uses a AA sized battery and runs exceptionally well on the energizer lithium batteries plus runs very well on eneloops and 14500 li-ion rechargeables. It runs so-so on regular alkaline batteries, but alkalines don't have enough juice to reach the higher output levels that the light is capable of.)
Since you have the Klarus (which uses either two CR123 batteries or one 18650 Li-ion rechargeabel,) you may also want to consider the soon to be released Zebralight H32 (which uses a single CR123 battery.) Very similar to the H52, and will be an outstanding performer.
The Coast headlights are not bad, but not great either. The flood to thow feature on them, however, is outstanding...but is the only outstanding feature they have. Everything else about the coast lights is sub-par such as not being water proof, the circuit is not regulated (which means the light dims over time instead of remaining constant like most newer lights,) they are flimsy (especially in the area where the light adjusts up & down,) bulky, heavy, & uncomfortable to me. I have to say though that I do like them, but I don't love them like I love the zebralights. The last coast headlight I bought broke. I exchanged it, and it has sat in a drawer ever since. I plan to give it to my nephew since I will not be using it again.
Good Luck, and let us know the answer to the question posed above about the performance of your 18650's in extreme cold (if you have ever used them in extreme cold up there.)