"How do I improve without working for it?"
Pray to god that he exists and gives you magical fingers.
"How do I get from point A to point B the fastest way possible?"
¯\_(ツ)_/¯
It's up to your brain and body adapting to the skill levels that are required for 8000pp.
You can try to force play the pp requirements over and over until you perhaps get the big pp play you need for 8000pp.
But this will require you adapt at an insane rate, your fingers will probably not be able to withstand the speed, your eyes will probably not be able to keep up throughout 95% of your practice. Will this be the fastest way? Who knows.
The other way to improve is to play slightly below the "too hard" difficulty and slightly above the "pretty easy, but not too easy" difficulty so your senses can keep up and actually process what you're doing while still getting to experience the harder difficulty and process that information to learn from and improve.
Somewhere in between those methods is your "fastest way". You'll have to figure it out by yourself.
