geometry chart would certainly lead one to believe that it's the exact same frame.

as for 2300/Sora vs 105... yeah... 8 speed vs 10 speed... I'd go the BD route. I had a Sora bike and it served me well, I liked the set up but the 105 is just nicer. Shifts smooter, faster, etc and having 2 extra cogs is nice. (I now have 105...)

$:$ you're getting more bike for your money, as is usually the case with BD. Even if you factor in the cost of having it assembled (you can DIY with basic tools and know-how) and the cost of getting it dialed in, you couldn't get a 105 bike at your LBS for the same total cost.