On power I will say with stock header and midpipe (aka both cats intact) , you will get 250 -270 hp on 93 Octane. So 300 is not going to happen unfortunately.
Coworth had done some solid testing when they did their kit and determined 280 HP is the safe limit for stock rods. Anything above is a lottery.
Oil ratings are universal. Most people chase power for track and hence go to a thicker grade oil. If you are using it on the public roads and are using the manufacturers tested tune (HKS) , then follow their instructions for 0W-20 or what ever rating they say. They have done their R&D. Change the oil more frequently and you will be fine. All the best.
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