I do track days too and although im no racer i like to have the assurance my tyres will grip, and i have to say my tyre of choice has all ways been the 207/208 / gps, they are expensive, but the current set have done 5 trackdays and a few trips here and there and still have life left, I also recomend the reinsports but i havnet used them on an NSR yet. I have used BT90's on a NC30 and they too were great! if your only doing a few days a year and around a 1000 miles get the GP208's there about 230 quid a set but you can pick up good sets of ebay now and then for around 60 quid,