The X9 is better than the X7. X9 is lighter than X7 and it also comes in the short cage version. If you can spend the money and would like very precise shifting, buy the X9. If you break derailleurs every week but still want something that shifts well and is cheap, go for the X7: so far so good in terms of my experience with X7 triggers and derailleur.
yeah i got the x-9 as well, but x-7 shifter. x-9 is the best, its burly, presice, and looks beautiful. So worth he extra money x-9 is the same as the x-0 interms of shifting quality and everything else xcept the material
There is not really any performance or durability difference in the derailleur. The difference is in the shifter. X.9 and X.0 shifters are zero loss. This means they initiate the shift the second it clicks rather than having to push thru the shift. The X9 and X0 shifters work MUCH better.