My old x40 competition scope was the most stable scope I ever had. I just put it down to the simpler construction, i.e. no zoom system and smaller overall dimensions.
In heat it was fine, unlike 20-50's but when cold i.e. just above freezing it would over range slightly but was predictable.
Worst scope I had for temp shift was an early EFR 10-40 where it if it got hot it focussed to 45yds then just didn't move so you had to guess.