The red/green spring combo is generally ment for buigger tracks where you need to let the motor spool up to a higher rpm. Your tracks seems to be smaller than an average track so I would stay with the purple springs. The reason for using the purple springs is to get the bottom end grunt you need when running in a heavy touring car. The Red/green combo will let the motor spool up easier and to a higher RPM, but it would lack alot of the raw power out of the turns to actually propell the car around the track.
Back onto the subject of gear ratio. The monster has a certain window it will perform best. I'm thinking you might be out of that window a bit. The window is different for every track, but there is a point where you can over gear a motor AS WELL AS undergear it too much. When it is undergeared to much the motor will be at high RPM and out of it's powerband more than what it would liek to be. Generally at high rpm motors are less efficeint and heat up.
My suggestion would be this, gear your motor to top out right before you turn at the end of the straight. Then check your lap times. If your laptimes are faster that what they were before then your moving in the right direction. Then gear for infeild punch and stuff. I always gear for the fastest lap times because thats all that matters in the end.
If you honestly have tried to get the correct gearing and maybe even change your driving style a bit, I would suggest purchasing our P2K2 based stock motor. It will have a powerband better suited for your application. It is a TORQUE based motor where as the monster is a RPM based motor.
I know figuruing out the best gearing and setups for motors can be frustrating at times. Trust me I know, because thats what I do all the time!!!
So please just give our product another chance. Hopefully what I have said will help you find the sweet spot in the motor. If you have any more questions feel free to post it here. Happy Racing.