Won't a 380mm rear make your fronts not work as hard and thus last longer?
Personally, I would only consider getting the 380mm rear if the calipers and pads were the same for both axles. In this case they are not so I'd go with the tiny looking 345mm kit.
2015 F34 328iX GT Glacier Silver
2011 E90 M3 Monte Carlo Blue
2004 E46 M3 Imola Red