First of all, Final Cut Pro X works extremely fast on my Hackintosh. It works much like Adobe Premier's Mercury Playback Engine. Footage and Effects are rendered in real time. This program is also easier to use that iMovie. That may sound weird, but it is much easier to acquire the clips you need at the lengths you want. Anyway, it's a great program that has a number of impressive green screen keying and luminosity effects that you just can't find on iMovie.
I am using this program exclusively, and it screams with my current video card. I am very happy with it. I chose the Nvidia 285 video card to work with the Adobe Mercury Playback Engine, but I am using Final Cut Pro X all the time. I don't even need Adobe Premiere, and Final Cut Pro X is so much easier to use. It works so seamlessly with my iMovie, iTunes, and iPhoto.
I will say that Final Cut Pro X was pretty buggy in the first version. It would crash for no reason at random. I was only working on short one minute projects, so it wasn't a big deal, and there was an autosave. After the Final Cut Pro X update, I have had no crashes, and it seems that Apple has worked out most of the bugs.
Thanks Apple for this great program