It's always based upon gross takeoff weight. The wrinkle comes when a PPL multi license holder, who, in Canada, can fly a Twin Otter, which is a 12,500 aircraft, flies it at it's permitted 14,500 for ferrying. Is he still legal? Oh, the complexities!
Canadian regulation:
401.26 The holder of a private pilot licence - aeroplane may act as
(a) pilot-in-command or co-pilot of an aeroplane of a class and type in respect of which the licence is endorsed with ratings;
So, if you have the rating, go fly whatever you are rated for.