[mwtrogus]

Just wanted to add that I just tried to install Berk resonated mid pipes on the N55 X1 and they don't fit. They are designed for N54 and N55 BMW 135.
I wanted to run these midpipes to remove the secondary cats. The Berk were overall about 3 inches short and the bends were not in the right places and our X1 must have a slightly narrower exhaust path than the 135. I actually thought that they would have been a much closer fit and my exhaust shop could modify to fit, but there was no chance.
Only option as I see it is to run a Y pipe off the downpipe (I have a catless AR downpipe) to bring it back as a 2 into 1 setup. A 3 or 3.5 inch single pipe. Maybe an inline muffler midsection and then straight pipe all the way back, into a true dual exhaust, quad tip.
just letting everyone know... downpipe for N55 fit, but not midpipe or cat back muffler.