Old MacPro (2,1) with Windows 7 runs extremely slow?
I understand you have a 32 bit EFI. I do not think this has anything to do with the BIOS. Since you have already installed 64 bit Windows 7, I am guessing it does not.

In your comments, you say you modified the CD. So I can assume you have a working DVD drive. When you say you modified, I assume this involved oscdimg.

Apple does not officially support 64 bit Windows on your model Mac. Well, I have a 2007 iMac, which Apple does not officially support 64 bit Windows, yet I have run 64 bit Windows 7 and I am currently running 64 bit Windows 10.

I assume the Windows 7 installation DVD has Windows 7 Service Pack 1 (SP1) or later included. This is a requirement according to the Apple website Install Windows 7 on your Mac using Boot Camp. 

You have to installed Windows for a BIOS boot. It not a question of whether you can install to use a EFI boot, but rather the restriction is in the drivers. The Boot Camp Support Software for your Mac assumes you are using a BIOS boot method. This software includes the drivers for your Mac. 

You can download the Boot Camp Support Software for your Mac from the website Boot Camp Support Software 4.0.4033. Since you have a 64 bit install, you might have trouble installing this download. If so, refer to the website Using Boot Camp Support Software 4.0.4033 to install 64 bit Windows 7 or 8.

Finally, you might not be blessed. If not, then your Mac would be slow to boot. Click on this link for instructions on how to bless your Windows 7 install. The instruction assume you have already installed the Boot Camp Support Software.


  Note: Many people have assumed the latest release the the Boot Camp Support Software should always be used. This is completely wrong. You have to use the Boot Camp Support Software released for your model Mac. Windows is designed to accept older drivers and even 32 bit drivers when the current driver is not available. So, if you decide to install 64 bit Windows 10 on your Mac, you would still use the same Boot Camp Support Software as for a 32 bit Windows 7 install.