low FPS in editor after update unity 5

in unity 4.6 (when not use remote)
300~400fps in editor

in unity 5 (when not use remote)

50~100fps in editor

it’s ok in build

what’s wrong???

Update I found out, that the reason my FPS was dropping was because of dust blocking the air flow in my laptop. As soon as I cleaned it out it worked perfectly.

i had the same issue, and found out that the reason is i used EditorApplication.update in some utility script of my own for updating UI in Editor,
after disabling that update i got max fps