I don't know how much my comments will help/hurt, but here you go:
I used to ride a lot. Never tracked mileage, but as I drive around the same areas of CT these days, I realize it was a lot.
Anyway, the best road mike I had was steel. It was a Univega Grand Sprint. I went in to get a grouppo for a used Vitus I was thinking of picking up, and after I rode this, I bought it. VERY stiff, but you could feel that every ounce of energy was going to the back wheel. I got more into mountain biking, and went full-hog on that.
I started out with an off-brand aluminum frame. 7000 series, so maybe not the best aloy for a bike frame, but the quality of welds, milled bottom yoke, square seat and chain stays and ovalized/rectangular down tube with gussets looked impressive on paper. Weight was low as well. But, the bike suffered from serious flex in the rear triangle. I would frequently use my 'granny' gear to climb with this frame in spite of the low weight, because a lot of frame flex was eating up my power. The components were absolutely top shelf. XT/XTR, Paul's brakes, Cook Bros cranks etc. It was stolen from my garage one day, and it was the best thing that could have happened! I order a hand-built Ibis Mojo that I still have. Steel, but lighter than the aluminum frame. No flex in the triangle, but not abusive. Tubing was 1mm thick in the center, single butted (to 2mm). A lot of the guys racing these bikes at the time wrapped the top tube with a piece of PVC pipe because the bars coming around in a crash would collapse the top tube! I never used the granny gear on this bike, and in fact increased the mid and large front cogs for more speed, because I could turn more gear on this bike. Night and day really...
What does this long-winded e-mail mean? Don't buy a bike based on the material or specs alone- you need to ride one. And, although Carbon is inherently stiff, properly engineered, it can have very controlled stiffness, which means a less abusive ride, with no power loss to the ground. When test riding, be sure to come out of the saddle in 'too-high' a gear and really *crank* on the bike. That is a good simulation of a steep hill, and you want to have a feel of that before you buy it- and riding around a bike shop parking lot does not replicate this well otherwise.
My friend just bought a new MTN bike (about $4,000.00 I think he spent), and with that he was able to rent it for a weekend before buying. It was a good experience, as he was looking at a 29" vs. 26" traditional MTN frame. That is something you have to try to decide for sure... Bottom line is, go visit your bike shops, check out whatever seems good, and listen to their suggestions. rent the bike (or bikes) if you can before you buy. If you buy the one you rent, often that cost can be applied to the purchase.
You may spend a bit more that way, but you will avoid owning a bike you could own for a long time that is not the best it could be for your taste within your budget. Also know that many shops might be willing to swap a grouppo around for you. If you 'dream' bike is too expensive, see if a step down on the grouppo would bring you into your price range... The mid grade stuff is so good 99% of people wouldn't notice the difference, and are a few grams of weight worth the huge jump in price? Generally not.
"Just because I don't know what I'm doing never stopped me before!"