Where are you based? I’m just building up a 16.5″ right now with a 120-160 adjustable fork. I’m 5ft10 with 32.5″ inside leg so almost same proportions as you.
The 18″ is a long 18″ if that makes sense. You or I could probably ride an 18″ happily for more XC based stuff, but I’m building this bike more biased towards quick blasts in the woods and throwing down the occasional DH track myself… Hence the fork as with 120 it’ll be perfectly balanced for general trail riding yet I can chopper it out for the gnarlier DH stuff. Dan Stanton does state it rides sweet anywhere between 120 & 160 mm, but personal preference will always have some bearing on what an individual goes for. As my bike is also to be a shop demo bike I thought the ability to choose travel was a wise one.
Only reason to go for an 853 would be that you’ve already got a very nice 1 1/8th headset that you insist on using, otherwise it’s more expensive, isn’t any lighter that you’d notice (an ounce or two tops) and you can’t run a modern tapered fork on it.