I used to run 9's for many years, then did the 8 of Chromag bars and found sore elbows. Moved to 10's and 11's (the Salsa 11's I gave to Syncro). Now running 15's and I like them a lot. Personally don't find any issue with the 15's on steeps, tech, or aggressive riding. Going to get a set of 16's mostly because the specific set is lighter and I am looking to build a lighter trail bike next.
15's from Hunter. https://huntercycles.bigcartel.com/product/hunter-smooth-move-low-rise-handlebar
16's from Corvus for future weight weenie build. https://corvuscycles.com/product/sweet-16-carbon-handlebar/