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Contemporary: Crowder's Ain't No Grave and This I Know are ones I'd like to try someday,
Traditional: O' For A Thousand Tongues, In the Sweet By and By, This is My Father's World, Come Thou Fount...

https://www.mandolincafe.com/forum/content/768-Out-of-Stock-A-Pandemic-Supply-and-Demand-Story

I thought this was interesting, and it might give you some answers.

Beard Instruments posted a list of soon-to-be-availabe instruments that contained an octave mandolin about a week ago.

I did a search for "Tim O'brien octave mandolin" and found some great live videos. (He plays different genres, including bluegrass and celtic, on different instuments, including mandolin and octave...