Fuel ecomony is not really any different, maybe 0.1 -+ 0.2 litres per/100km depending on driving style. I have a fairly heavy right foot though and rarely drive hwy klms.
I average about 9.8litres/100klm on a tank....at least that's what the on board computer is indicating.
I've tried settings 7 through to 10 but found my X5 tends to flat spot when accelerating hard with no advantage in power or torque.

Just try it and see how you go?