FWIW, I took a look through many fonts that are naturally narrower than Arial in an attempt to address Bluto’s concerns about Noto Sans SemiCondensed. I was very sorely tempted by Myriad Pro, which at the same height and weight was only slightly wider than Noto SemiCondensed and was a stylistic close match as well, but at least for now I’ve decided to stick with Noto Sans. Also, I learned some stuff. At least for Noto, Condensed is 20% narrower than Regular, SemiCondensed is 10% narrower.
So if this whole thing blows up on me, Myriad Pro may be my Plan B. But that plan looks a lot like an iPod commercial 😉