i have been using penrite(HPR 15, 15w-50) ever since i bought the car at 70,000kms....it has minor mods, 10psi, r34gtt SMIC, exhaust..... and its daily driven i pull around 700km a week.....and change the oil every 5000km's......
I have tried using motul turbolight 4100, and yes i do agree seeing a difference, car seems to be a little bit more responsive.....but at the end of the day....since my car is a daily driver, and i pull massive km's a week, penrite for me does the job well....and never ever had a problem with it....total cost $45($35 for oil, $10 for ryco oil filter)....
I recently tried penrite HPR30 20w-15, due to the summer heat and i want to reduce burning oil, and it proved to be too thick and the car was a complete slug.....so drained it out and used 15w-50 penrite HPR 15, and back to normal.......
So the grades will also determine how responsive the car will be