well id say just find a company (if offbrand) that u either have known someone to use and make the power u need....or ask the company if they have a flow or effieciency chart for the fmic...thats what i did

as far as piping goes...i forget all the positives and negatives but of course aluminum is lighter than steel (stainless/mild/etc)...remember w/ steel that it MAY rust if condensation/water gets into yer piping sumhow which would ruin the integrity of the piping...ummm i remember reading sumthing about one being better for heat transfer/or not bein affected as much by engine bay temps but i cant remember which one it is...also mandrel bends are best (as w/ most things flow is only gonna be as good as yer most restrictive/smallest point..hence no crush bent muffler shop piping...i mean u can use that but i wouldnt...probly not a HUGE difference tho

im sure some other people have more/better info