There's really no true answer. A lot of people will say yes, you'll have some trouble simply because all things being equal, you're trying to push a heavier bike than him, so you'll be slower. But sometimes, weight doesn't matter if you've got the fitness level. I would probably say that it'll be a little harder for you, but if you're super fit, I wouldn't put too much thought into it. You can always change the tires and wheels on the Motobecane. Every little thing helps to keep the weight down.

Steel bikes are just heavier. I've got a Surly Cross-Check, which is also exactly the kind of bike you're looking for. Tourer/commuter/CX, it does everything, all you do is change the tires! But it's decently heavy too. I'd recommend checking that out - it's cheaper than a Trek 520. You can see and test ride them at West End Bikes. I'm a short small guy, I can't ride fast because I just don't have the muscles for it - but on a calm day I can ride pretty consistently around 15-16mph. With wind at my back about 18-20, more if I really try, and with wind in my face, down around 12-13.

Honestly, I'd just get 2 bikes. Get a decent mid-level CF bike, like Giant Defy Advanced or Specialized Roubaix (both around $2k), then get a cheap used bike to commute with for a while until you save up to afford a nicer steel commuter like the Cross Check or the Motobecane - then the weight issues doesn't matter.

I had the same thought as you - which is why I got my Surly, and while I've done 2 MS150s on it, I'm now saving to buy a CF bike because it's just too hard for me to push a heavy bike that distance and try to keep up with other riders. I used it to commute some days, but I also have 2 other steel bikes I commute on.