well the simple answer is I thought they would be better, you see I don't have a stock exhaust fitted, the gen 2 has a Motad 2 into 1 and the gen 1 has Black widow headers. aftermarket pipes tend to be single walled and have a wider (deeper) trumpets for the gasket. these give more crush room and fit way better, when I found out they could be had for such a cheap price it became a no brainer.Why do you go with the bigger sized ones than listed just out of curiosity?
several owners have used these on stock exhausts and reported they are easier to fit and give a better seal than the thinner stock ones. although TBH the difference is only about 0.6mm.