I have done a zetec turbo conversion, running on megasquirt efi. I converted my cvh to cossie management first, that was a bad experience. I then got shut of the cossie stuff and converted to megasquirt on the cvh, then got shut of the cvh.

EFI will give you more reliability and accurate fueling, better economy if its mapped well. You can also have features like launch control, anti lag, boost control etc etc.