Originally Posted by LowCel

Do you have any trouble climbing in your easiest gear? If not then you really don't need the 27 on the back and you can get by with an 11-25. If you do want easier gears then go with the 11-27, you will have to purchase a Shimano cassette though. Shimano and SRAM cassettes have the same spacing so it will work fine. I am currently using Shimano cassettes on both of my bikes which are both SRAM equipped.