Utility
Neither the BMW 328 nor the BMW M3 has a marked advantage in terms of seating capacity.
There's no clear winner between the 328 and the BMW M3 with respect to hauling capacity.
Performance
With that kind of horsepower, the BMW M3 is a legitimate sports car.
In terms of horsepower, the BMW M3 packs quite a wallop and will knock the BMW 328 down a few rungs. However, keep in mind that high horsepower engines often command higher insurance premiums.
Dimensions
The BMW 328's tank is about the same size as the M3's, though the BMW M3's is slightly larger.
The BMW 328 and the BMW M3 compete for the same parking spaces.
Convenience
You'll most certainly have to take the BMW M3 for a fill-up more often than the BMW 328 because of its tank size and fuel economy.
Cost
The BMW 328 will save you money at the pump compared to the BMW M3.
Producing an accurate gas mileage evaluation is so tough that some think not even the federal government can do it, but it looks as though the BMW 328 is the winner as far as fuel economy.
The 328 is tremendously less expensive than the M3 regarding MSRP.
The BMW 328 will save you a lots_of_money at the pump every year compared to the BMW M3.
The BMW M3 will cost you a lots_of_money in gasoline every year compared to the 328.
Handling
With their comparable turning radii, the BMW 328 and the BMW M3 most certainly handle about the same into and out of tight spots.
Drivetrain
The BMW M3's engine is considerably larger than the BMW 328's. Keep in mind that more massive engines may use more gas than smaller ones.
The BMW 328 could learn a lesson or two from the BMW M3 with respect to torque.
The M3 packs quite a punch compared to the BMW 328 with respect to torque, which is roughly equivalent to acceleration.
Warranty
The BMW M3 and the BMW 328 have the same basic after-sale protection.