I think AWG sizes are as follows,
True Stranded AWG Size ID" IDmm
1/0 0.406 10.3124
2/0 0.461 11.7094
3/0 0.512 13.0048
4/0 0.591 15.0114
SkyHighCarAudio 1/0 0.53 13.5
SkyHighCarAudio 2/0 0.63 16
If that's accurate, the SHCA 2/0 should be >4/0 sized with the SHCA 1/0 being about 3/0 awg. I'm guessing anyone running welding cable would be closer to the true AWG standard sizes, car audio sizes are very unregulated
thanks for the update big ben