Ive got a GSR with 90,000 miles and I run Castrol Syntec oil with Honda oil filters. I have an open element air filter (AEM intake) and drive the car about average (as gentle as I do hard). Should I be changing the oil every 3k or can I make it 5k without any problems? It's just that synthetic oil is really expensive so chaning often gets expensive, but with a high time engine I don't want to do anything that is going to cause me probems in the future. Thanks for the imput.