k30lls

Hi, I have an 07 Atom Legeng R size 0 It currently has a 155 reserve and electra 170 main. I am looking to downsize and wanted to know what is the smallest sabre2 I can fir in. I will be buying a sabre2 150 now but can I go smaller in the future. I am not sure what the pack volumes on the rig are. thanks