Sig 365XL

I have been looking into getting a polymer frame carry pistol and narrowed it down to the Sig 365XL or the Sig 320. When I go to price them out I'm seeing about $500 range between the 365s and 320s. Not 365 vs 320 but 365 vs 365 and again the 320 vs 320. I'm also seeing extra wording added to the description like "Legion" and "optics ready". Anyone got a dumbed down explanation for the different 365s and 320s?