The SRAM X-9 rear derailleur and SRAM X-9 shifters are a great combo. They use a 1:1 shifting ratio and a powerful return spring that makes for really easy installation, adjustment, and maintenance.
We used this system including the SRAM X-9 trigger shifters, SRAM X-9 rear derailleur, SRAM Hollow Point Chain and a SRAM rear cassette to replace a Shimano XTR drivetrain on a bike that had had chronic shifting problems. It has shifted flawlessly ever since.
I was pleased to discover that the SRAM X-9 rear derailleur doesn't clank against the chainstays on downhills like my Shimano derailleurs sometimes do. This is a really a nice feature, especially on FSR rear suspension frames. It makes for a much quieter ride.
Another positive of the X-9 rear derailleur is its direct cable housing feed that doesn't catch on branches as much as non-direct cable routed designs.
The SRAM X-9 rear derailleur and SRAM X-9 shifters make for an excellent upgrade. You will, however, have to get both the shifters and the derailleur if you don't already have a 1:1 shift ratio system such as another SRAM product.
