I have two bikes. One cheaper Shimano equipped 21 speed mtb, and a much nicer 24 speed. Seriously I don't feel there is all that much difference in the two drive trains. I modified the 21 speed with a 48t front sprocket group for commuting with and its great. The other is running 42t in the front and 8 on the back smallest being 12t. 24 is nice, I don't see that 27 would make it much better. I don't even see the need for 10 at the back so 11 just seems overkill for the sake of it.