I picked up a Sora crankset a few years ago. Heavy! You could use it for a sea anchor. 105 coud be slipped onto a top racers's bike and if no one saw it, it might well go undetected. 105 is good stuff. Sora is heavy and osme of the metal used is very low grade. (I've dropped chains and mangled Sora chainrings.)

Edit: My best bike has a 105 crankset. Radically better than the Sora. IN fact when I bought it I compared it to a used Ultegra with the same hollowtech cranks. Went 105 because it was in better shape, the cranks were identical and the slightly inferior chainrings are a wear item.

Ben