Not trying to be smart, but have you thought about getting good sport tyres for your GT-P's instead of going straight to an R-compound tyre? I'm assuming you may have done one or two track days but if you haven't then exploring the upper limits of grip for an R compound would mean you'd have to be pushing quite hard to get them to squeal/lose grip pending the conditions of the day ect. I've attended track days where guys on sports tyres have been noticeably quicker than others on semi slicks as road tyres can offer a greater feedback to learning lines and technique before going straight to outright grip. Just my 2c