I I'm 5' 11" with about a 33" inseam, shorter torso, and longer arms. ... Found a Kona sizing chart that said for someone 5'11, the 19" is the right size, and a 20" is for someone 6' 0" to 6' 4".
Since you're only an inch away from being 5' 12", you might be able to go either way, depending upon your preferences.
Does your shop have any other Kona bikes in the 19" size for you to try? Trying some other model in 19" wouldn't be apples-to-apples, but it might make for a useful experiment.
FWIW, I'm 5' 9", and right at the top-edge of the range that Specialized gives for their 17" frame size. I just built up a 19" frame bike as an experiment, because I feel my riding style is such that I would benefit from a longer top-tube and a slightly reduced seat-to-bar drop. I am one inch below the recommended, 5' 10" starting point for a 19" frame, but so far I like what I've built. Today will be my first real ride on the bike though, so you might want to hit me up in a week or two for a long-term opinion.