I went through 4 sram XO blackbox carbon rear mechs & 200gs would have been a lot better. sram are ultra fragile, I've got 7yr old M950 r.mechs that have taken more abuse & work better.
I dont love the cosmetics of M970 r.mech, certainly all polished finish M900 was a wise move, a black rear mech is going to look scratched up & tatty in no time. havent had any problems in operation with M970, certainly the wider pivots should mean it lasts even longer than old faithful M950.