I've heard the focus does well with cam timing adjustments. But the Focus Zetec cams don't have any kind of notch or any marks to tell to where the stock setting would be. You'd need a dyno to actually tune the car up because you can never be exactly sure how much advancement or retardment you're doing. This is what I remember reading about that. As for me, i never felt like buying the cams and paying for the dyno time was worth the gains it would provide, although I'm sure others on here might think that it is way worth it. I don't know man, depends what you are going for.
in order for you to install both cam gears, you would have to bypass the VCT. Tom had a kit to do it, dont know if he still offers it. i do believe that you can run an adjustable one and retain the other oem gear to have the VCT intact.