It is, honestly, not nearly as bad as you'd think. The weight should be pretty well distributed, armor doesn't have to be all that heavy to stop a sword, and the gambeson is doing a lot of the heavy lifting for piercing weapons. Blunt weapons, well, those are going to be unpleasant pretty much no matter what. You get really hot though; there's a reason that the Saracens did such a number on the crusaders when they were able to get them outside of cities.

Wearing a plate carrier is, IMO, worse than wearing a gambeson and chain maille.