86 RockHopper,2008 Specialized Globe. Both upgraded to 9 speeds.
I'll assume it's a MB with 26" tires?
IF SO, basically it should be very good, but you could probably "tweak" it a bit with a bit more of a "road" cassette. I doubt the cost would be worth it though.
Maybe something like an 11-21? That would give you a bit more "top end" and a bit more closely spaced flat cruising gears. The downside is that you may have to shift to the small ring more often and the bike would have to be equipped with a Compact FH to accept the 11T cog.
Other factors would also be in play, such as how steep are your hills and even crank length. 5MM difference in crank length can sometimes have a much greater effect than a 1 tooth difference on a cog. Going from "fat" knobby tires to "skinny" street tires can make an even bigger difference.
Even if you occasionally "spin out" on the 12T, it probably won't really effect your top speed as much as you would think.
'''96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '12 Surly Pacer, All are 3x8,9 or 10. It is hilly around here!
Unless your hills are incredibly steep and long, the gearing sounds unnecessarily low. A 22x27 low gear (21 gear-inches) is extremely low and probably over kill for any but the weakest rider or a very heavily loaded tourer.
The 42x12 high gear of 91 gear inches is probably adequate for flat terrain but could get spun out if you luck into a tailwind.
I agree with Bill Kapaun that a more road-like cassette would make the gearing more useful. A 12x23 or 12x21 cassette would keep the same high gear, still give a plenty low low gear and provide finer steps in the middle gears.