Consider the bicycle to be a constant, dynamic, work in progress. Start with a cheap bike with cheap components, and then upgrade as you feel the need or have the funds. You're buying your ultimate bike one component at a time this way, and you end up with lots of spare parts that can be useful later. At some point, you'll even upgrade the frame. When this happens, you only pay for a new frame, and you just move your old components onto it.
A few minor points: avoid SRAM cranks and bottom bracket. Their external bottom bracket has a VERY flaky manner of attachment. Shimano makes the best external bottom brackets (Hollowtech II) with the best method of attachment.
Usually, the next to top of line component group is the best value for money: Shimano Ultegra, Campag Chorus are pretty much the best value. After that, it's diminishing returns. What you're actually paying for is the envy of others, and even then, it's only those who can tell what it is. Not a good reason to buy more expensive stuff. Yes, the pro's usually use the good stuff, but they get it for free and they get paid to be photographed with it. But if you fall for this, then next year you'll have to upgrade to the new top of line. Like right now, if you had Dura Ace 7900, you would need to upgrade to Dura Ace 9000 due to peer pressure.
Me, I just ride a fixed gear for everything, so I couldn't care less about the latest gruppo. Upgrade-wise, I'm up to Campag Chorus brakes with Record levers, but I switch back to Centaur for the winter commuting season. But even now, after having the current frame for over three years, I am still constantly upgrading components little by little. It's one thing that makes cycling fun. To have the ultimate bike all at once makes absolutely no sense. What do you do to upgrade?
The smartest thing that bicycle manufacturers ever did was to standardize on head tube diameters and bottom bracket threadings. This allowed all component mfrs to make standardized products, broadening the choices available. But once they start going proprietary, it ruins it for everyone.
Luis