how on earth would the mkx run better on xbone? i don't think there are any games that run better on the xbone than ps4. i think it's too early to tell because the game's not even finished/optimized, but if you watch that 45 minute mkx video from brazil, it looked like cassie's xray was slower than the rest, and maybe quan's looked a little slow compared to his trailer. but they kept switching between consoles because of controller batteries getting low.
mk9 had slower xrays on ps3. it didn't look that bad because you could more closely see bones breaking, but the framerate still dropped like hell. i don't expect this to happen on the ps4, but i wouldn't be surprised if it happens on the xbone or if the devs intentionally decrease the framerate for xrays to 30 on xbone.
are you saying NRS is making the ps4+xbone version and the other 3 are being ported by a different company?
ps3 was designed to be difficult to develop for in an attempt to prolong the console's life and make sure that games would look better over time as the devs learned how to develop for it, but they ended up favoring the more familiar 360 and ps3 got stuck with all the crappy ports. sony fixed this horrenoud defect with the ps4. the xbox and ps consoles have switched places in that regard.
