Which scope would be best for a 300 BLK with a 16" barrel?
You need to give more information about what you plan to do with the scope. Instinctively I automatically think about an LVPO, and have a 1-4x24 scope on my 300 blk, but you might be using yours for something entirely different than me. I have a short 7.5" barrel and plan to use it to shoot pigs. I don't see the subsonic rounds in 300 blk being an advantage unless you can use a suppressor. Where I live I can't (YET!).
I just ordered the EP8 1-8x28 for my 8.6 blk. There is a 4-6 week lead time on the delivery though, so that might be something you consider. Arken currently has a 25% discount using code: SAVE25%
I have no affiliation with Arken, just a customer and don't have the scope to give a real world review. 8.6 blk in supersonic will definitely shoot 800-1000 as dkrat243 mentions, but I personally won't take game at that distance. Most all of my game will be taken within 300 yards, even with 8.6 blk.
How about a bit more information on what you use your 300 blk for and/or what you plan to use it for?
Since the 300BO operates in the subsonic range, I would suggest an EPL4 4-16 or 6-24. You won't be shooting 800 to 1K, so the 4-16 is more than enough scope for that application.