Hi this’s my only post in english, I hope it will be helpful!
I’ll show you how to fix the lag on Macbook Pro retina.
First, this issue is probably a software problem. So I hope that Apple will patch this quickly!
To fix the lag you need to disable the HiDPI on your current resolution.
For this, two ways are possible.
First possibility (Didn’t work for me!)
Download Xcode in the AppStore
Run it and go in Xcode menu => « Open Developer Tool » => « More Developer Tools »
Log in with your Apple ID and download « Graphics Tools for Xcode ».
Open the .dmg
Run « Quartz Debug » and go in the « Window » menu and open « UI Resolution ».
Here you need to disable the HiDPI option, logout and show if the lag is fixed.
If the lag isn’t fixed try this (It worked for me!) download SwitchResX, it is a 14€ software.
Run the software from pref panel and choose a resolution without (HiDPI) like this:
Now the lag is fixed!
PS: Sorry for my english 😉
Version française ici