I am looking at a '04 Bianchi Axis that is size 55. I am mountain biker looking to expand my horizons and help out with my endurance. I am 5'11" with a 31 1/2" inseem. Do you think the 55 will fit? Should I hold out and order a 57? Do 2 cm make that much difference? I have always riden L mt. bikes for Specialized and Santa Cruz. Please help ...