I have a Vishnu Procede Rev2a tuning computer on my 2008 335i.
Experts, like COBB Tuning, show zero gains in their testing (
http://blogs.cobbtuning.com/category/vehicles/bmw/335i/), for normal boost situations.
When the boost is increased with a tuning computer, the gains increase a bit, as can be expected. Vishnu indicates that you can expect at least 5 hp increase.
But when the boost is increased even more, e.g. when you have a Meth kit, you can expect real (two digit) gains (
http://www.n54tech.com/forums/showthread.php?t=13765&highlight=intake+testing).
So, is it a waste of time to use an aftermarket air filter for normal boost situations? And only necessary for higher boost situations?
From internet information, it also seems like their is no practical performance difference between all the aftermarket brands. Although prices vary considerably.
Comments from 135i/335i owners with tuning computers will be appreciated.