can we expect any major or considerable difference in the performance once the firmware update is released for the wp8.1 DP with rest of the world?
My experience is that the system appears a bit snappier, battery seems to last more too, but only without Cortana. Apart from that, there is the usual stability, smoothness + the things Microsoft has added to improve the OS that really help make it more usable. I haven't one single complaint on pure performances to date. It's on par or better than 8 and maybe better than many Android top end devices. I don't have workbench suites but in terms of perceived experience WP, is still better than Android and on par with iOS in this specific area. That's only my 2 cents.