You should find that all of those combinations come to a very similar, if not the same n1 values.
The aeroplane needs x amount of thrust to do the job, any one of those combinations (if correct) should do it. Therefore the fan will be spinning at the same (or very similar) speed.
As to which one actually is the best for costs etc, that would depend on the operators individual maintenance programme etc. I.e Your operation may be penalised for using 26k as opposed to 24k for example.
Last edited by donkey123; 22nd March 2013 at 21:55.