For the 10 rounders... it depends on how far it extends out of the butt of the grip. The pistol must be able to fit in a box, the dementions can be found on the IDPA website.
I shoot a Springfield 1911, and the the pistol with the 10 rounders will not fit the box, so I use the 8s. I use the 10 rounders for USPSA and shoot the Limited-10 class.