I don't think you can go on stats for either weight or thickness of armour from IA or other fluff - because I don't think GW 'get' it - if they did the turret would be bigger to accommodate the breech of the gun, and also the silhouette would be lower.
What I look at is in-game comparison. Front armour equivalency of the Land Raider means this is one heavy MBT. I think of it more like Merkava in terms of weight, as opposed to lighter than a Sherman. That sort of classification I give to the 'Stegs' or whatever in the Dan Abnett books.