My chainrings are 53/39 and my cassettes are 13-26. On group rides I'll ride up to 20 mph on the 39 without cross-chaining. Looking up the road I'll decide whether to stay on the 39 or shift up to the 53. Likewise if I'm on the 53 I'll ride it down to 18 mph and look up the road then decide whether to stay on it or go to the 39. Some of the steeper hills will drop me below 90 rpm but I always get back above 90 soon after, even when I'm tired. Many years ago I learned that a higher cadence helps develop stamina and keeps these old arthritic knees and ankles going.
No way would I trade my 39 for a 42.