Just a heads up on something that I don't think has been covered in this thread regarding the factory tune and 93oct.
Here in New Zealand we have JDM imports, there are are number of STI's factory equipted with the ej207 running on the stock tune on 95 or 95ron which is equvilant to 90oct and 93oct, Yes they do knock. (I usually see upto 6 degrees on all the cars I have looked at.) But at the same time the ecu does its job and pulls timing accordingly, Most cars I look at have the IAM at 16 with Learned knock in the upper load region.
The main point of this post is to tell everyone that yes it will knock (this has been covered before)
but these cars are lasting upwards of 120,000miles (We don't have a huge number of high ways so average miles for a car is 10-12,000 per year.
Some of these cars even have a downpipe and still run the factory tune, the ecu is smarter than most think.