All it is, is GT5P with a few extra tracks. There are no new confirmed cars in it, just the same amount as in GT5P.
The only major difference you will noticed is extra detail, like detail in the car's head-lights, which you will not even bother looking at.
GT5P is already detailed enough. All you are getting with GT5 is a few extra tracks on time trail, and minor car damage -which is not really important to hard-core racers, only the racing is. So you may as well stick with GT5P and ignore GT5.
The only major difference you will noticed is extra detail, like detail in the car's head-lights, which you will not even bother looking at.
GT5P is already detailed enough. All you are getting with GT5 is a few extra tracks on time trail, and minor car damage -which is not really important to hard-core racers, only the racing is. So you may as well stick with GT5P and ignore GT5.