Get either one.
Then save up and get the other if you feel you want/need it.

That's basically what I did: I purchased a Cannondale CAAD 10 earlier in the year. I really like this bike and hope to do some shorter races with it.

But I also hope to do some longer rides, centuries, etc. Could I use the CAAD 10? Sure. But I don't feel like always messing with the stem, or adding/subtracting a bag, pump, light, etc. depending on what I'm doing that day.
Lazy? Maybe. but I also wanted a bike with compact chain ring (50/34). The CAAD is 52/36.
With all the hills in my area, I want something more geared for hills. Also wanted a bike with a more "endurance" geometry. I'm selling some stuff to help finance the expense, so it's not that big a deal for me.

...plus, I figure these 2 bikes total what some pay for 1 full CF bike.
Eh, I'm just excited to have found the sport and want to enjoy it fully (on a budget).