I recently bought a Mac Pro off eBay from a company that custom rebuilds them. I bought one with a Titan XP for heavy motions graphics. When I bought it the titan xp was on back order but needed a replacement for an iMac I fried, so the company sent me the tower with a stock GPU and then sent...
I've just spoken to MVC (MacVidCards) and he has the EFI ready to go on the new Titan Xp. He just needs to test it with the Web Driver when its released next week. Looking good! Here is the link to his blog
http://www.macvidcards.com/blog/nvidia-pascal-coming-to-macs-efi-already-in-the-works