help me understand models within a group

Hello all,

I am venturing out of lurking to ask if someone(s) will explain to me how it works. I've been checking out the specs on different manufactures models within a line (ie, Dolce, Ventura, Dama, etc) and do they all have similar components in a given price range? And the difference between manufactures primarily in the geometry of the bike?

My goal this year is building up my milage on my bike before I buy a new one. And really any one I chose will seem like a 'creampuff' compared to my current wheels (a 43 pound Schwinn Varsity :). I want to several cycling events in 2013 that have been a dream for quite a few years.

Thank you in advance, I have learned so much just reading these threads.

Oh, and when I start testing my possibilities, I will be considering bikes up to $1500. I don't want to take any out for a spin until I am ready to plunk down my money.