Windows 10 Pro Insider Preview Build 10547, Minecraft 15w39b, Java 8 u25
Surface Pro 3 Core i3 model
If you use /setblock to place 2 end gateways on top of each other in the overworld and stand in it, it causes a huge FPS drop.
Not standing in the Gateway: 60-80 fps
Standing in Gateway: 1-6 fps