I'd follow these simple rules
1. What fits you the best, Cannondale is going to have totally different geometry than Specialized. Get a bike that FEELS right first and foremost.
2. Get the best components within your budget
3. Weight the options of where the money is best spent: The Allez Elite is a wonderful bike. If you can save $600 over the Tarmac, think about what you can do with that $600: Buy a nice set of shorts/bibs, shoes, helmet, gloves, etc etc. Don't buy the more expensive bike, blow your budget and then not have enough money to buy the gear it takes to actually ride regularly in comfort. Because if you do that, you won't want to ride
