DUO AND DUO2 are both great. Nemesis is different as it needs to be geared down about 3-4 teeth less than the Duo to be consistent throughout the whole run. I've noticed quite a few people avoiding the hassle associated with the Nemesis and just sticking with their Duo/Duo2 and getting awesome performance.
If you are running the Tekin RS and want to be super fast, get a LRP x-12. Game Over