I can't speak for 5'-8", but for 6-5, 31" pitch is nightmare material. I simply do not fly any carrier that doesn't have some kind of Economy Plus, Economy Comfort or whatever they call it. Life is too short.

No matter how tall you are, 32" is better than 31" and 34" is better yet. As for 17" width, that is also pretty narrow. If you are slender it won't be terrible but if you have any girth, it will be tight.

The original designs for economy seats were based on measurements from test pilots decades ago. Since those guys tend to be on the small side, young and in excellent condition, we got tiny Y seats.