I'd still strongly suggest checking out the CAAD9. You can get a far better deal on eBay, but if it's your first bike, buy from a shop and get fitted.
The CAAD9 also should hold up it's resale value quite well if you want to upgrade in a year or two.
I'd rather go with the CAAD9 w/Tiagra than the 2.3 w/105. FYI in previous years the 2100 was 105, the 2300 was Ultegra.