I was able to get some very large cells this year also. I have monitored them throughout the season and have found they are also the same size as queens from other cells.
I believe the larva can only eat so much royal jelly, and the rest is eaten by the worker bees once the queen emerges. Although when virgins hatch in the incubator I have observed them going back into the cells and eating the excess royal jelly.
The larger cells in my opinion are a result of the extra royal jelly and not to accomodate a larger queen.