i was looking for it as well but today i find that something bout that 2000cc 6cyl not are not cheaper to maintain then a 2500cc 6cyl..
reason is 2000cc 6cyl some of the electronic parts are using siemens rather then 2500cc using bosch electronic parts mostly..
the siemens electornic parts are much more expensive..parts like sensors and ecu's
might be wrong but this is what i get when compare for e34 and e46 models..