Well outta interest one day, I compared my Catco 'high flow' cat to my stock cat and its basically identical to except the Catco has 3" flanges instead. The honeycomb density is identical. The Catco's body is actually a tad smaller. I fail to see how its a 'high flow' cat at all!!! 3" flanges vs 2.5" doesn't make it 'high flow' IMHO.
Needless to say as an experiment I put a straight pipe in its place. Haven't looked back. A couple of dB more noise but definitely better performance. Here in SA every second car is a rusted POS/carby powered car so one more car with no cat makes no difference (only gets driven twice a month). Yes I'll be buying a Metal Cat in the very near future so save the flamage.