This bike searching process is not as easy as non-cyclists would think!

I'm a pretty new cyclist who got into cycling because I want to compete in duathlons (running is my main activity). I've been thinking whether it would be better for me to buy an endurance bike first (like say the Cannondale Synapse) or just bite the bullet and by a racing bike, comfort until I start racing be damned. I've looked at a couple Cannondale CAAD10 bikes and they look nice.

I certainly cannot afford to buy two bikes right now or in the near to mid future so for at least a year I will have to use the same bike for everything, long rides and races if I get around to racing.

If you were in my shoes, what would you do? Would a racing bike be comfortable enough for group rides and/or would an endurance bike be aggressive enough for racing?