Trapways on the Caroma are in the 3" to 4" range
Some have plastic parts in the trapway, some are porcelain
Parts have been dependable
Toto Aquia CST414M
Toto is 2-5/8", part of the trapway is plastic.
Parts have been dependable
Gerber is porcelain, 2-0"
Parts have been dependable, a little more work when it needs repairs.
Performance between the three is really pretty even.
I think the Caroma and the Toto look nicer as far as the quailty of the pour.
Trapways are all glazed, even if its just a clear coat to seal it.
I don't think that's a factor, what is a factor is the design itself and how well they maintain the shape of it as the clay dries.