R0GUE, it's optional, you can choose EFI during the install process, but I'd recommend it.
I have experienced much better system performance with EFI. I know the reason why.

With the use of EFI, RC2 is able to use the apple stock kernel and kexts, and they work very well
together, as they are concerted. Selecting GUID + EFI and the proper chipset and graphic
settings, will give many systems a perfect out of the box install.

Also, read some other posts about EFI that I posted into the Discussions, I think I was talking about
improvements compared to PCBIOS.