My first bike years ago was a 58. The LBS sized me right between a 56 and 58. I always regretted getting the 58 and every bike since has been a 56 and one is a custom with a very extensive fit process. I'm also 6' with a 32 inch inseam.

You might try a search here. Someone once did a survey of posters height and size and 56 was most common for 72 inch height.