My current bike is a Medium Size frame with a sticker on the frame stating that if your height is between 5'8'' and 6' the bike should fit you. I ride it a lot (55 kms RT daily commute to work) I don't feel that the fit is perfect but it's ok. I've bought a bike for parts and the frame size is XL (58cm) I wonder if it would be a better fit for me. By the way I'm 5'11''.

Thanks