The trunk of the Pontiac is only 11 l bigger than the Peugeot 407. However, the difference is not significant and it would be right to say that both vehicles have more of less the same trunk space.
Pontiac Grand Am V Coupe 2.2 i 16V 141HP manual has 7 millimeters longer wheelbase when compared to the Peugeot. A longer wheelbase gives more stable and comfortable ride, especially when driving fast. It also gives more storage space. However, cars having a longer wheelbase will not be as maneuverable as those with a shorter length between its axles.
The Pontiac Grand Am V has 192 cc greater engine capacity compared to the Peugeot 407 Coupe 2.0HDi 163HP manual. For the reason that the difference is little, the Pontiac Grand Am V Coupe 2.2 i 16V 141HP manual should accelerate only slightly better, of course if other paramerters are the same.
The higher a vehicle is, the better is the comfort of getting in to it and greater capacity of putting massive amount of thinks to it. The difference between these two cars at the level of 3 millimeters to the advantage of the Pontiac Grand Am V Coupe is little and should not be really noticeable.