Take the rpm is whichever gear takes your fancy @ 100kmh and multiply it by 1.09. BTW you cannot get 4.11 for our cars only 4.09.
I changed my old ute from 3.73 to 4.09 and it does make the car laggier in 1st as the lower ratio takes load off the motor, this really only applies to manual cars tho.
I've been toying with the idea of 2.93 ot 3.02 for my F6 and locking out first in the ZF unless you come to a complete stop. The car is much nicer to drive with no 2->1 downshifts but is a touch laggy to drive around only going down to 2nd in scenarios like rolling up to at slow speed (but not stopping) at a round about or intersection.