Those of you with single chainrings, what cassettes are you using? I'm going to lose the front shifting and am looking at the IRD 12-30 with a 39 up front. How does it shift compared to Shimano stuff? I'm running a 12-25 right now and never need big ring and only occassionally wish for an easier gear. Are there any other manufacturers of 10 spd shimano compatible cassettes?