Can Anyone Help Explain Why My Friend's M5 Feels So Much Lighter Than My Z4M?

Whenever I drive his E60 M5, it always feels like it doesn't weigh anything at all, compared to my Z4M. The response is immediate and the car feels more forgiving.

Is it because his car has more torque? I'm kind of a newb when it comes to torque and horsepower, sorry.