Regarding the smashing of the boost pipe, apparently prawn (correct me if I'm wrong) did this and he had problems immediately after. Ive also done it, i didn't get any problems but i also dont remember hearing or feeling a difference. You can buy those boost pipes without the baffles so its smooth all the way through.
If you are however going to smash it anyway, Id recommend setting it all into position, ready to be smashed then go have an argument with your other half or try n do something that you can't quite do so you get really angry then quickly go and smash the crap out of the baffles cos they are as hard as Klitschko's face!