Handling
With their comparable turning radii, the Mazda MAZDASPEED MAZDA3 and the Mazda MAZDA6 indubitably handle about the same into and out of tight spots.
Drivetrain
The MAZDA6 has a more sizeable engine than the Mazda MAZDASPEED MAZDA3. Note that smaller engines typically get better gas mileage, but smaller engines can be stressed more.
Torque equals pickup, and the MAZDASPEED MAZDA3 will have picked up and gone by the time the Mazda MAZDA6 finally gets moving.
The Mazda MAZDA6 could learn a lesson or two from the Mazda MAZDASPEED MAZDA3 in terms of pickup.
Utility
Neither the Mazda MAZDA6 nor the Mazda MAZDASPEED MAZDA3 has a marked advantage when it comes to seating capacity.
Convenience
You'll doubtless have to take the MAZDASPEED MAZDA3 for a fill-up more often than the MAZDA6 because of its tank size and gas mileage.
Comfort
While the front cabin in the Mazda MAZDASPEED MAZDA3 offers a bit more head room than the Mazda MAZDA6, there honestly isn't much of a difference.
The Mazda MAZDA6 is not particularly more spacious for your passengers than the MAZDASPEED MAZDA3.
Dimensions
The MAZDA6 is a tad more ponderous than the MAZDASPEED MAZDA3.
Your wallet will hurt more every time you fill up the Mazda MAZDA6 than the Mazda MAZDASPEED MAZDA3 because of its larger tank.
The MAZDASPEED MAZDA3 and the Mazda MAZDA6 compete for the same parking spaces.
Cost
The Mazda MAZDA6 doesn't pale in comparison to the Mazda MAZDASPEED MAZDA3 as far as gas mileage.
In terms of gas mileage, the Mazda MAZDASPEED MAZDA3 and the Mazda MAZDA6 don't differ much.
Regarding MSRP, the Mazda MAZDA6 costs approximately as much as the Mazda MAZDASPEED MAZDA3 (though the Mazda MAZDASPEED MAZDA3 is slightly cheaper).
Overview
The basic after-sale protection that comes with the Mazda MAZDASPEED MAZDA3 isn't quite as generous as the Mazda MAZDA6's.