Impossible to say.

Will the BMW parts guy give you the correct one if the "normal" one is the wrong guess?

Neither SHOULD give you major driving issues- cams just stay put in "safe" mode, so maybe rough idle, little worse performance. Just wait til it codes, read the code, but the intake or exhaust as required. (ASsume you have a 6cyl....IIIRC, V8s have 2 for each bank)

Or, replace both intake and exhaust.... OEM parts arent that pricey.