Mike,
I have the AR Design catless downpipes, they sound great with the rest of the stock exhaust system, not too different at idle but as soon as you get on it, it sounds great
If you buy them though make sure you ask for the ones that fit the RHD cars, as the O2 sensors are in slightly different places, got mine shipped direct from AR Design without any hassle and fitted myself, although fitting them is a pain lol
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M235i Auto: Alpine White / Black Dakota Leather, Brushed Aluminium / High-gloss Black Interior, Driver Comfort / Professional Media / Sun Protection Packages, Harman Kardon Hi-Fi, Enhanced Bluetooth, Lumbar & Heated Seats, Adaptive M Sport Suspension