hey ,
I bought a Lumia 1520 just last week , and wierdly it was on developer preview with lumia black, so I used Nokia Software Update , and it installed Lumia Cyan ( I didn't use wp8 :'( ) Anyways, battery isn't as good as I expected but it's Ok )maybe it's wp 8.1), the phone is fast and smooth , but lags ONLY when I'm using Internet explorer and then jump to start screen, there , theanimation lagss, just searched on google and someone wrote that when he unpined Cortana from his homescreen it became smooth again, and that's what I did and It worked !!!!! so go try it
I bought a Lumia 1520 just last week , and wierdly it was on developer preview with lumia black, so I used Nokia Software Update , and it installed Lumia Cyan ( I didn't use wp8 :'( ) Anyways, battery isn't as good as I expected but it's Ok )maybe it's wp 8.1), the phone is fast and smooth , but lags ONLY when I'm using Internet explorer and then jump to start screen, there , theanimation lagss, just searched on google and someone wrote that when he unpined Cortana from his homescreen it became smooth again, and that's what I did and It worked !!!!! so go try it