BTW Peter I warped two sets of the standard 305mm discs on the track with a standard GTA previously, without trying so hard to do so! The weather was a little warm perhaps, and Mondello is notoriously hard on brakes.
Assuming you have already bought the 305mm calipers - I'd suggest at a minimum getting upgraded discs (e.g. cross drilled or grooved), if the theory you are investigating of using larger discs with the 305mm callipers is flawed.
In honesty though Alfa seriously underestimated the extended Braking power required for such a fast car - that engine is just superb!
How near is the launch date of your new baby anyway?
TB