Rs3's aren't available in proper sizes for 19" M3 wheels. I would buy Yokohama AD08's in 255/35/19 and 275/35/19. It's a great tire and those are ideal sizes for ZCP wheels IMO.
'04 E46 M3 - Jet Black - Sold
'08 E90 M3 - Alpine White - Sold
'13 E92 M3 - Silverstone II - Sold
'13 E92 M3 - Alpine White - Ohlins TTX, Fall-Line Suspension Arms/Bushings, AP Racing BBK, OE GTS Aero, Cobra Seats, Akrapovic GT4, GMG 4-point, BBS E88