I have 8 gigs of ram, first generation mac pro 2X2.66 Ghz Dual-Core Intel Xeon, an Nividia GeForce 8800 GT 512 video card and still Motion is crawling. I have disabled all effects, set the renderer to draft and the resolution on the screen to a third...Is there something I am missing? Some setting that will free this thing up and make it scream in real time? It is choking like a dog.
All we know at the moment is the 3870 seems to be the current rage.
Scroll down a few pages and you will see the same question asked many times. This is the current favorite but we have no real idea if it will help in any particular combination of hardware, OS, and file types.
Motion is, for the most part, all about unrealistically high expectations, a marketing position. You get used to it or you go back to another product like After Effects that behaves within expected parameters. Even if they're not any better than Motion's at least I know what to expct!