All the CAAD models currently available are CAAD9 frames. Cannondale then distinguishes them by a second number. The smaller the number, the fancier the components. So the CAAD9 5 is a bit more expensive and has some nicer components than the CAAD9 6, but the same frame.

The CAAD9 is the 9th generation CAAD frame. That's all that number means.

As for "105 components," Shimano makes several lines of road components. They include

Dura-Ace: pro-level, light, best materials.
Ultegra: Good for serious amateurs either rec riding or racing. A little more plastic, finishes might not be as fancy, usually bears a resemblance to last year's Dura-Ace.
105: Mid-level, generally considered the entry level of the "serious" component groups.
Tiagra: A level below 105, but has considerably improved its quality over the last few years and is a good, solid beginner group
Sora: Another level below. Still OK for general purpose use, but you might find components wearing out/breaking a bit more often, materials aren't as nice, lots more plastic, less durable.