Regardless of system specs, I've driven the 2015 STi, and the AWD system is not lacking in any way. It's the best chassis that the STi has had yet, by far. It has "only" 305hp, but it can finally really put every one of those ponies to use. More power is always appreciated in a car like that, but to me the only thing that Subaru really needs is the hatch body. That said, they insist that the take rate is too low to make it viable. I really wonder about that.
This RS is probably very comparable to the STi in terms of performance, but it kills it with respect to appearance and lack of a trunk.