Reading the latest message makes me hypothesize that some of you think that have an EFI32 won't allow to use the 64-bit capabilities of the Mac Pro's Xeons, while EFI64 allow.
Have you ever thought on how many -bit uses the old-fashioned BIOS?
According to the Wikipedia article on BIOS, it's compiled as 16-bit code, and in first system was used to communicate directly with peripherals. Later with evolved systems (32-bit or more), that part was assigned to drivers, but the BIOS remained always 16-bit.
Even now modern PCs that are equipped with XP64/Vista64/Any 64-bit OS have the same kind of BIOS, that is responsible only of booting, bootstrapping, clock and low level hardware-related system settings. And that OSes are able to run 64-bit code.
So, have an EFI32 doesn't mean that you can't run 64-bit executables, instead you can. For example, if you have Xcode locate its .app, get info, and deselect the "open in 32 bit mode" option, then launch it and check on activity viewer that it's really using 64-bit capabilities. Under the Kind column you'll see "Intel (64-bit) and under the Virtual memory column you should see an extremely large amount of memory available to the app.
I think that by the time Mac Pro 06 was launched the first implementation of EFI was EFI32, so apple used it also because not all of its systems were 64-bit. But the thing I can't understand is why Apple refuses to update the "old" Pros with an EFI64 code, which as stated in previous posts shouldn't be difficult an expensive.