Jeremy Clarkson said it best "BMW at their best is still not up to Porsche at thier best," or something like that along the lines.
Back when the the 911's (996) and M3's (E46) were racing in GT3, BMW couldn't match the 911's, so they went in and made a M3 GTR-V8, which according to the rules was not allowed, Porsche had protested stated that the cars had to be production based, so BMW made a few batches, then the FIA ruled that I believe 1,000 engines had to made.
Hmm, but Porsche had made in the late 90's a 911 GT1--a 911 that was mid-engined, having nothing whatsoever to do with the actually 911.