Lag is still present for me. Wunderlist, rotating with keyboard up, some games, etc. I've seen no change.
I changed my display view from "standard" to "zoomed" and turned off transparency. I see no lag whatsoever system wide.
this does cut down lag for me ALOT but then no advantage to getting the 6+ compared to the 6 as you aren't using 1080p
First apple device I have used that has let me down this way! Steve Jobs had the right attitude with his hardware and software...