No, his car is a US spec M3, blown. It's not a 328i / is.
The 328 rear diff is a 2.93:1 unit, but it's also generally an open diff, and not a limited slip diff.
Also, the bolt pattern is different on the input shaft, and the gearset is a little smaller. I'd be highly surprised if somebody swapped in a 328 rear diff, as top speed would still be restricted to 173 MPH with those numbers.
It's the stupid way to build a car...how often do you accelerate as hard as possible, and how often do you get to exceed 150 MPH? The first one I can see quite often (which is why the Euro models offered 3.64:1 and 3.91:1 rear diffs). Around Toronto (or anywhere in NA for that matter) you rarely (and shouldn't on city streets / highways!) get to see 150 MPH+. Even on a track like Mosport, you might see 150 MPH+ ONCE near the end of the backstraight.
Even if you were building the car as a racecar, you would have gone shorter on the rear end, not taller. We've had supercharged US spec M3's at Mosport before, and they don't max out at the end of the backstraight at Mosport in 5th gear (157 MPH) with the 3.23 rear diff. Doubtful this kid is going to either...
So I agree with SF, and I'm calling BS on this one.
I'm not really an asshole, I just play one on the Internet