Please take nothing I said as anti-Allez. My comments are based on a buddy of mine riding one, and it was awfully hard to see significant difference next to the Sirrus (he is my size). I do think he may have bought a size too big, which may jade my geometry comments a bit.

You know you better than we do. If you know you really want a road bike, then get one. You'll get fewer looks on your group rides (this from personal experience). If you know the Sirrus isn't your long term cup of tea but you keep it for now, focus your spends on portable items.. cycling computer, clothing, even good wheels are portable.

I just don't want you to think a road bike will be a quantum speed leap. You could ride the Sirrus until your averages are in the 18-19 range, and then make the switch, and would potentially see more gain (as aero is the limiter at those speeds). But even then, 3 mph is big.. like 15% jump big.. like 30% more wattage (as a WAG) big.

And if you do go road bike, see what your local shops carry in your price range, test ride them, and then post specific questions about models here. You will get specific feed back from owners. I could tell you know how good Felt bikes are, but with no dealer, it wouldn't help you.