that would depend on how much your planning on shooting. I think the sandB loading is a pretty cheap round to use for plinking, that is until SSA comes out with the TNT loading that should be around 13 dollars or so a box.
Isnt the magnet test refering to steel core bullets like a armor piercing round? Are they refering to whole cartridge or just bullet? I know no one makes steel cased 6.8 but that would be odd for the 7.62 and 556 shooters that cant shoot steel cased ammo.