Mine came with 42T and it was OK on Tarmac but of off road hill, it was not great. I tried 40T and it was better but the difference was not significant so I move to 38T which is good I only got stuck once on a 15% Mtb trial (muddy wet rocky...). It did not bother me much, getting stuck and forced to push 50m over a 80km MTB ride, I can leave with that... but I know that I would had done in with a 34 or 36 as I get through it in dry conditions.
I had to change my chain was the supplier sent a chain which was 1 linkset too short
as the a 36T chainring is cheaper than another chain I fitted a 36T ring.
Compared to a 42T, the 36T x 10-42T is equivalent to 42T x 12-49T. As I very rarely use le 10T, I figured out that if I loose the bearly used hardest gear (42x10T) to get something like a a eagle (42x50T) cog, it is beneficial for me.