ive never used the io/7, but ive had a couple pairs of the io/s. the ioX is bigger and a different frame system but nothing to different from my ios. i love my ios, so you would be 100% fine with the iox. as for the photocromatic lense.... Totally worth it in lowlight, but worthless in super bright conditions. for instance, night skiing the lense worked great. but later in the season when i was standing at the top of jackson hole, and it was 4pm, and the sun was super bright, i couldnt see crap. i was squinting and the sun was so dang bright my eyes were watering. i was literally skiing blind ( lol kind of dangerous) SO if you want good performance in intense sun, get a reflective lense, but for good performance in stormy, dark conditions the photocromatic are totally worth it. It just depends on what conditions youll mostly be using them in. good luck