X9 is worth the extra I think. I’ve just, bit by bit, upgraded from x-7 to x-9.
For me the key benefits are:
Shifters: X9 do feel nicer and have a detatchable handlebar clamp so are matchmaker compatalbe
Crank: X9 are in 2-piece so you can slide off the chain ring spider and use CNC’d direct mount chainrings – the best way to go if you’re going 1×10. They’re also hollow crank arms so (supposidly) lighter (I couldn’t really tell by the hand scales.
Rear mech: just much better quality. My X7 mech broke on me after about 3 rides – the cast body just broke just below the mounting bolt. I just went straight to an x9. Also x9 is available as a clutch mech which is a worthwile upgrade even if you’re not running 1×10