By using the rear clutch as your main take off point to upgrade starting with a 1500 RPM torque spring is best bet.
Your stock spring is 800 so the combo of 10-11 weight sliders makes a huge difference.
If you go all out and get clutch and clutch (NCY, Dr Pulley) bell and torque spring as well as a high performance variator and drive plate you can go heavier on weights around 12grams and get more top end and lots of take off.