I’ve been running a 10 speed double all season (no bashguard), and had run a double on a 9 speed set up for the last 3 years.
I think it’s perfect, I’ve played with various ratios, but liked 40/28 with 9 speed and now have 42/28 with 10 speed, find I stay in the big ring 90% of the time, and just drop for the steep stuff. To that end I’m probably going to try a single ring next season.
I think the 11-36 cassettes really do facilitate the use of a double for most riders without any real loss of gears, reckon the SRAM 39/26 would be spot on for most ‘trail’ bikes.