I got this news letter from Autospeed.com today and read their excellent article on the BMW M5 V10 engine.  http://autospeed.com/cms/A_111534/article.html
The stuff they do today on high end production engines are just amazing.
4-valve infine variable exh and intake cam timing, hydraformed SS exhaust manifold, 4 oil pumps where one of them is continuosly variable, 10 individual electronically controlled throttle bodies..
What can a tuner do to improve this without messing up 100 parameters in the process ?  Not much.
Lay one finger on this package and a whole range of CPU's will curse you forever 200 billion times a second.