[135Pats]

Are you planning on running a more aggressive tune? If not, there’s really not much of a reason to delete the primary cats, or put another way it’s probably not worth the hassle and cost. FBO N54s without a tune dyno at somewhere in the neighborhood of 300whp, granted your 1M is running more aggressive mapping, but it still it tapped out below 15psi (someone please correct me if I am mistaken). At that type of boost, IMO the upside of downpipes isn’t really going to be realized, and as you pointed out they are not without flaws (smell, smoke, noise for some people, rasp, cost of installation). There does not appear to be a consensus on just how “high-flow” the OE downpipes are for the 1m, they do appear to be less restrictive, but I haven’t heard of anyone running a true FBO type tune/map with those downpipes on.

Long story short: If you don’t plan on running a tune to take advantage of what catless downpipes offer, there’s little reason to switch. Use the money towards a better FMIC, which is totally lacking from the factory on all N54s. In the UK the advantages might be mitigated, but during the summer months your car will thank you.