Commercially available 6.8 SPC ammo can be safely fired using any of the 3 chamber profiles you mentioned. Some ammo manufacturers such as Silver State Armory (www.ssarmory.com
) sell "tactical loads" that are loaded hotter than original SAAMI specifications. You need an SPC II or DMR chamber to safely use this ammo.
The SPC II and DMR chambers also allow you to load your own ammo hotter than you could with a SAAMI chamber.