Shonen, I think I covered 25k daily driving when I had my gtr. While its not a pain in the butt driving it on a daily basis, some roads are pretty unbearable. I blame the reasonably stiff factory vspec suspension. Other than the stiff ride, Ive had no gripes driving my gtr daily.
The only thing I can say, is that once I had it modified (larger than stock turbos), I lost a fair bit of mid range power, which made it less practical for driving at normal city speeds. For a street car, I think both Nick, Paul, Kris and Jerry have done well in their turbo choice
Oh and in relation to the topic, I had my car tuned for 100 RON fuel. I took it out to oran park and while I had extreme in the car, my knock levels did not exceed 30. The car had great power and smooth response. I then tanked up on optimax, and noticed an increase in knock spikes, up to around 40-45. Id suggest using extreme to be definitely worthwhile. The car should run smoother and knock should be reduced. You can always have a play around with timing on the pfc