I ended up buying a cheap one from Online Automotive for £109 delivered.
Got it fitted today.
It does sound slightly louder (in a good way) than the previous vauxhall one. It was a bit loud before anyway, because of the remus centre pipe.
Didn't take the pre-cat out. However, the pre-cat that was in there was only half the size of the vauxhall one, and the holes were a lot bigger.