I'm not so sure it's as complicated as the marketing spin tries to make it. The bikes in every brand's lineup are basically sorted by material and groupset quality into various price points. At the lower end you have aluminum with a couple of lower end and mid level groups, in the middle you have heavier carbon with low, mid and higher end groups, and at the top you have light carbon with higher end groups. Pretty much it comes down to how much you want to spend on a bike. Some brands will also throw race geometry and "comfort" frames into the mix, so you should try out those to see what fit you prefer, then make the same choices on frame material and group.

If you want a chart, here's one that pretty much lays out the concept:

http://www.bikesdirect.com/products/road_bikes.htm