Here's a website that publishes comprehensive factory specs for almost any car.
www.zeroto60times.com

More specifically, this page will give you information about BMW models back to 1968 to current models.
BMW 0-60 Times & BMW Quarter Mile Times | BMW E36, X5, BMW M3 0-60, M5, M6, M1, 330, Z4 and Cabrio Bimmer 0 to 60 stats!

Aside from any mods, this should answer most questions regarding performance comparisons, for example; I was able to compare a 2000 M5 vs. a 2002 X5 4.6is.

This information helped me decide about a few upgrades I was considering. I wanted to add an ESS supercharger to my 4.6is to bring my performance level close to a stock e39 M5. According to the charts and the information I gathered about the supercharger, even this 100hp+ upgrade would not get anywhere near the M5's 0-60 times of 4.6 sec!

Oh well... Maybe I should just keep my X5 4.6is stock and buy the M5?

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