I think -2.5 on the Hankook RS3s are tad too much but its close. I'd recommend about -2.3 to -2.4 on street tires.
I too will try some NT01s this weekend. I will report back as well.
2013 F30 328i Melbourne Red
2011 E90 M3 Monte Carlo Blue
2004 E46 M3 Imola Red