If anyone else goes for a X before the cats, try to get it made to look like this one. I spoke to one of the designers of this pipe for a Porsche 928 (also a V8) and he says the crucial elements are the wide entry angle of the exhaust from downpipes, the narrow exit angle before the cats, and the size of the crossover and the distance from the header.
He found moving the X just a few inches forward or back lost some of the power gains.
Of course I have no idea if my X is in the right spot as it was not placed based on dyno testing.
http://rennlist.com/forums/928-forum...pping-now.html
http://rennlist.com/forums/928-forum...sale-sold.html