The 120mm/80mm BCD on the XX is proprietary too, it just doesn't look as funky as the FSA. The significant difference in my eyes is just that SRAM stuff is likely to be around longer. There is no new standard for 2x9s yet so everything is going to be proprietary (unless you jump back to the old 94mm BCD 5 arm cranks). Personally I would go with the Middleburn Duo, but i'm not so stuck on external BB's 