On a standard car, adding a panel filter(K&N), yes there are differences. Added intake noise, added throttle response, from lower down the rev range( tested via time trails,and was quicker accelerating). Downside less MPG,like that matters ;)
Maybe but what I actually wanted to buy is a straight through pipe,removing the second cat, to the rear box, to fit the oem system. Cant find one though off the shelf ! Going to purchase one tomorrow, will double check between both systems mentioned !
Well i'm in the same boat as the OP, my centre section is split, and the baffles are shot to bits. 95% sure going to order Milltek system and decat pipe.
With H&R's (30/40) fitted with cup suspension, the ride on A roads is great. As for B roads, you just avoid potholes,cling on to the the stearing wheel, give it beans, bounch a fair bit, and enjoy the fact your driving a gocart !