This is the stock rom for the S4 Google Edition phone that went on sale yesterday.
It is blazing fast. My LTE even works better. I also have about a gig, I think, more free space than on Samsung's stock rom.
If you want to try it,
Download ktoonsez's kernel for TouchWiz
Download SuperSu for rooting
Put all 3 zip files on your sd card.
If you don't have a nandroid backup already, make one first
Wipe everything (see this post if you have TWRP
Install the rom. Don't reboot
Install the kernel.
Wipe Cache and dalvik and reboot.