hi Deren,
i am in the same boat at the moment deciding on what to upgrade to. i am leaning towards the 2860R-5 because they seem to fit the response/power balance i am after. also they are currently only $2450 del from slide i have a friend who imported some HKS 2530 through greenline a while back and he tells me that he did pay a tax on arrival at customs, about 10% on top. i know what you mean about the gaskets- i have been quoted roughly $300 from nissan for everything required. so if you factor that in they end up very similarly priced....
hope that helps, Mike