What is your final gearing?
I´m not a pro, so don´t put much weight on my words, but I´m saying this just to give you something to think of.
It is very important thing to jet your carb´s good. That is one safe way to keep piston temp down.
Another thing is to gear it up and load the motor enough.
Sorry my english lol!
When you are on 6th gear and getting RPM´s up, don´t let your motor "think" it was/is an easy thing to do. Let it work hard.
Avoid over reving it for a long time.
I don´t know how to say it better, but I can give you an example. My final gearing can give me a top speed up to 100mph or a little over, but in real life it can only pull 96mph on a long long asphalt strip. So my motor needs to fight against wind/air with my heavy ass on it.
Hope this makes sence, if it doesn´t, ignore it.