Black Label tends to have the slimmest fits. But it also really depends on what item you're talking about. Many Polo Ralph Lauren items fit perfectly well on slim guys as well. It just depends on the item and your body type.
In Norway we have Ralph Lauren with classic fit, custom fit and slim fit. I want the slimmest one, what is this compared to when ordering from Ralph Lauren online? And what is custom fit compared to on the US sites?