The 6mm AI Forster dies were the second tier of pricing, not sure about the 6-06. The 06 brass is more plentiful and cheaper than the 6mm. No fire forming is needed for the 6-06, except that I think all cartridges need fire forming to fit the chamber, it is not required though. The 6MM AI you will rarely have to trim them.

I have not loaded for the others but the 6mm AI , 240 Weatherby, 6-284, & 6-06 are all in the same general velocity range +/- 100-150 fps based on pressure tested loads.

The smaller the capacity the longer the barrel life in some cases double from best to worst.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli