question of how much power are down pipes and test pipes are worth versus gutted main cats and precats. Well in his case I would say about 35RWHP. Ofcourse this run was at 1.5Bar versus 1.38 so subtract about 15RWHP which is really to much to subtract but then you have a gain of 20RWHP or about 25 HP to the flywheel.
I have down pipes on my car and when they went on all I could say was wow! People down play the down pipes because of troubles with installing them or fitment. But once you have them all you can wonder is why you didn't do this before.