When I bought mine, I was looking for the rpha 11 also, and the seller told me exactly that, for cb upright position, just have the rpha 70.it all depends on your riding style and bike the helmet is great for what it was designed for but when you ride 140-160 kph on average ear plugs are a must no meter the helmet but for a more up right bike i would not recommend it because off it aerodynamic characteristics.
( from my own experience its very un comfortable on upright naked bike)
Also it has a retractable sun visor which the 11 didn't have...