What do you mean? The Option Stream Z's pp actually goes fairly high, its still enough to win the 650 pp races.
According to this http://www.mygranturismo.net/car_sheet.php?id=698 -- assuming thats not a hack or a lie, the highest is 623.
From my experience its possible to win those races with cars at low 600+ pp range so you should be able to use the cars you like.
no one has a tune for it and it accels ok but to corner you have to crawl thru the turns and the Rabbit BMW GTR has a 25 second lead
The Option Stream Z was purpose built for going in a straight line at the highest top speed possible, it's not made for cornering. It's not far short of being a long distance dragster.
so no chance of using it for a 650 seasonal?