I recently test drove a 97 540i. Compared to my 500E, I wasn't too impressed. It seeemed to be about as fast off the line, but seemed to lose thrust higher up the rpms, where, of course, the 500E shines. Couldn't stand the seats, and i like the old recirculating ball steering on the MB.
Just my opinion. compared to the 400E, I'm sure its a bit quicker.

Tom
92 500E