I'm not sure if the new version is any different but anandtech
did bring up the issue of low framerate while scrolling in some webpages. It was really noticeable when I tried it in the store.
Even the 15in has trouble with low framerate sometimes too.
I don't know maybe the intel iris (I think 5100) is a substantial improvement, the only review I found on anandtech was for 2012 version which had the hd4000. Or maybe the performance increase from haswell has helped.
Either that or it is something I don't run into. I don't play games really but I haven't noticed any frame lag when scrolling.