Intake won't really get you any power so the obvious place is going to be downpipe. Downpipe will add 10-20 hp depending on how much you believe in manufacturer testing. I had the Fabspeed downpipe on my M235i and it's a great piece of equipment, but I don't think it added 20 hp. It did create a great soundtrack though.
As for IC that counts more towards being able to consistently put out power. Not calling the guy/gal a liar, but 370 hp to 424hp on chargepipe, IC, downpipe, etc seems optimistic to me without an ECU tune.
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