Fortuantely I haven't had to buy a road bike for years but I'd imagine when you are talking about the difference between a $700 Giant / Specialized and one $1500, the frames are probably very similar but the components are your biggest difference. My 2 cents suggests buy a bike with a 10 speed cassette, and with at least Tiagra. Tiagra will keep you going for a few years (more actually), and with the initial 10 speed cassette purchased bike, you can upgrade / replace with ease.