You probably don't really need 1080 at 60 for your finished projects but since you're just starting out with Motion, you need to lower your expectations. A long way. 1080 is about 2 million pixels per frame, DV is only about 400,000. That's not just five times as many pixels for the Mac to track; everything in video is exponential.
Explore the training tutorials available by Mark Spencer. You will get an idea of how his super powerful machine reacts with the software.
Adding a light roughly doubles the processing time over flat scenes. Two lights increases processing again. Reflections require processing the lights and then calculating the reflections so add another quarter of the time required for flat scenes. Add camera movement, motion blur, and depth of field and you need exponentially more processing time for every frame. The preload of renders into RAM is one of the cooler features of Motion, as comapred to After Effects, but that takes tons of time, to.
Try working in ye olde DV resolution for a few days. Get to know the software's limitations and what gets imposed by your Macintosh. Step up to 720p/30 and see how things slow down.