I had lag and I was able to fix the issue. I have a Lumia 1520 with cyan firmware, and by unpinning the Cortana live tile, I was able to cure the lag. That was able to do the trick for me. Though the web browser has improved with this update, when I go and browse certain websites like wpcentral.com they are laggy, and not like before. Other websites that were not WP optimized like theverge and Engadget render much clearer and nicer. So there are pros and cons, but it is quite frustrating that wpcentral website is so laggy now, I'm considering to revert back to cyan, because I think we need to wait for the next firmware to get announced so that gdr1 will be able to perform better.