Mac Pro keeps rebooting when installing Win7 on Mac Pro using EFI Boot/GPT drive I've tried to re-install Windows 7 using Bootcamp Assistent, since Windows 10 gave me a lot of headache.

Ran in to the error "No bootable device detected...", so I used following steps:


Make EFI bootable USB installer


Download Win10 install ISO
Boot into Windows DVD setup to access a Windows command prompt
open command prompt at install screen by pressing shift+F10
load diskpart and make clean install disk by typing:

diskpart
list disk
select disk n #n=USB stick
clean
convert gpt
create partition primary
format fs=fat32 label=Winstall quick
exit
exit

mount downloaded install ISO
drag everything from the mounted ISO onto the USB stick
delete bootmgr and bootmgr.efi from the stick to avoid BIOS/CMI boot and force EFI boot

Flash MacPro4,1 with MacPro5,1 firmware

Bootrom MP41.0081.B07 (EFI 1.4) to Bootrom MP51.007F.B03 (EFI 1.5) (If your machine shows Bootrom version MP41.0081.B08 you could first try to continue without upgrading. I don’t know which Apple EFI version is contained in there. Downgrading should be possible as well, definitely possible to version MP41.0081.B07. Please research if you don’t want to lose the downgrade possibility to MP41.0081.B08) The upgraded EFI finally enabled me to complete the boot process and you will have all other advantages of the 2010 and later models (hex-core CPU, faster RAM, Audio over DP) This upgrade is reversible. (If using El Capitan you need to disable System Integrity Protection. Otherwise the flash will not perform. If patch is running successfully you can see a big grey loader bar and the apple logo. Optical drives will open.)


Download MacPro5,1 firmware here -Mount .dmg (to prevent error 5570)
Download Mac Pro Firmware Utility here
Run Utility and follow instructions
check upgraded bootrom version and identifier in System Information

Setup Windows with EFI Boot


remove ALL physical drives except the to be Windows drive
plug in Winstall USB Stick
Boot Mac holding option/alt key
Choose EFI Boot
Enter setup and select GPT target disk
Install

Install Bootcamp Drivers (optional)


Boot into Windows
Download Bootcamp Support Software
Run Setup



The problem is, however, that my machine gets stuck in a bootloop during Windows 7 install... After initial installation, it tries to reboot but gets stuck at grey screen and keeps rebooting. When upon rebooting while holding option/alt key, the Windows drive does not appear, only the 'Winstall' USB stick.

Is this a Windows 7 issue and should I try Windows 8/8.1?

I plan to use drives as followed:


640 GB HDD (old OS X install)
500 GB HDD (Windows7)
240 GB pcie SSD (Main OS X)
"Windows 7 x64 (64-bit) will NOT boot natively using UEFI on a Macintosh!"

See source with technical details here:
https://darobins.wordpress.com/2009/10/04/native-uefi-windows-7-boot-on-mac-mini/

PS
It would have been nice to not only copy and paste my installation guide in your question. That cost me some time to put online. A link or reference as source would have been nice. From the title of my post it could have come to your mind as well, that a WIN8 or WIN10 installation had been the goal, not WIN7...EFI Boot Windows 8.1 or 10 Install on MacPro4,1 / Mac Pro (Early 2009)