I believe I'd let the type of hunting I was going to do trump the geography and geology of an area I was going to hunt when deciding between the different machines available. Both the units in question can handle tough ground. If the ground is too bad to detect with either of them , you probably need a PI to begin with. If you're hunting relics in the boonies the Deus is designed for just that and has the better abilities in the iron although the CTX is certainly no slouch with the small coil. If you're going to be trying to pick coins , gold and silver jewelry out of the canslaw and modern trash , the FBS machines are the tickets , rivaled only by the V3i for saving you from digging the whole place up.
The type of hunting you're going to do has the same type of influence on the coil size. Sure the 11 is most likely deeper regardless of the soil---some fraction of 2". When XP comes out with their small elliptical we could see a real game changer--if we can afford it