Sorry but it's a real mess. Bugs all over GT7 parameters , mainly gearbox. Try to find to way to enter each ratios till final drive. You can to try to catch the speed , but you will not have the PP... PD have to fix this urgently. Till this , patience.
You're right . The PP system is very smart and could be the best way to race any car against any other.
The problem is that it involve a lot of complicate mathematics . For the moment , lot of fails and bugs. Sometime you can drop 20PP for your one clic. Or they fix everything and we will a perfect game in some years after the job is done , or they take out the math for some parameters to have a working fair Performance Point , all this for the next 1update or 2.
-Gearbox ratios have to stay out the PP
-Camber / T.O.E / suspension / Ride height have to stay out the PP too.
All the rest is very good and a lot easier to calculate. Just my 2cts.