"And, oh yeah, I’m talking regular plain old perlon accessory cord, not Kevlar, Spectra, Gemini, or Titan cord. " Excel is good at removing "w00t".
I wouldn't have any problem with the strength of 5mm for my personal prussiks, but for crevasse rescue, I'd want 6 mm because you can exert more force than body weight using a 3:1 Z-Pulley. To get the necessary grip on 8 mm, you might have to go with a kleimheist.