Hard to say. It depends on your bone structure as well as your height.
If you have a low level of body fat, at 5'7", you can look pretty muscular at even just 11-12 stone. More than that is getting fairly big. I would guess that there aren't many 5'7" tall guys who are much heavier than 14 stone without either a) carrying more than 12% body fat or b) using 'roids.
You can also look decent at ten stone though - look at welterweight boxers; they are normally around 5'7" and look good at 10.5 stone (66.5kg)