Why not dump it before the cats?

IMO, because you give up the benefits of the x-pipe and the scavenging effects from one cylinder bank to the other. The link suggested a quantification of those benefits, with no reported downside. I don't know if that is the right figure, but I have been suggesting that anything you do in terms of dumping it out to atmosphere should be after the two sides are tied together, ie after the front silencer.

Yes, I read and understood the can't lose opportunity of the X pipe and have noted and logged in your suggestion but wouldn't pre cat dump be better with nitrous than going through the front silencer restriction? I assume the silencer is restricting.

Restriction issue is overblown, IMO.

Thanks for your input, very helpful