That's pretty good. I go through a lot less with lubrimoly than I did with Castrol, and I'm not sure if that's necessarily a great thing or not.
1k miles per quart of oil is the official rate.Lots of factors, but generally short trips or not a lot of time at full temp will contribute to increased fuel and less evaporation for the oil intern giving false burn rate. This can also lead to excessive or accelerated wear.
Longer trips or longer times at elevated temperatures will reduce/eliminate fuel and induce evaporation. So the way people drive, oil type/spec and general wear of engine has huge factors of burn.
These engines are high performance engines and high rates of burn are and can be normal. There is an official acceptable burn rate from BMW as well somewhere on the board.