I've tried 94 octane on the 328i for a period of time and found no performance improvement compared to 91 octane. I've since stayed with 91.
The only difference I've felt is using 94 octane on my Carrera. The manual recommend 93 but dealer stated its okay with 91 if performance isn't a concern.
Flav, with a chip upgrade, I can understand the need for 94. However for stock engines, 91 is all that is required.