Hybrid or Road Bike? I was given a Raleigh Venture comfort bike as a gift a few months ago, and took to riding very well. I am overweight, but dropping quickly. I started at 275 and sit around 250 now after two months of regular riding and a changed diet. I'm quite certain I've outgrown this bike. I struggle to maintain a good speed, usually managing just 11 or 12 mph, and the bike dealer I've been talking to says upgrading will be a tremendous difference, between better tires, lighter frame and a lower riding position.

The speed is frustrating, as this past weekend I took a 30 mile trip, which took over 2 1/2 hours. I stick to the roads, and in S. Florida they are in pretty good shape. So it would appear to me that a road bike is the way to go, but I'm still overweight, and not overly young anymore (37), so I worry maybe my back will hurt?

As a frame of reference, a dealer recommended the Trek FX series as being a little lower than a normal hybrid bike, and I'm looking specifically at the 7.3 FX. With my budget, if I went road bike, it'd half to be the 1.1 from Trek. 

My main question is road versus hybrid, but I'm also certainly open to manufacturer suggestions. I am very new, and not about to customize anything, so it has to be a bike that I can buy, not a bike I buy and then change a bunch of stuff. That's not me (yet).
Firstly, 11 or 12 mph isn't that slow, especially if you're still working on improving your fitness. Try measuring speed in kph instead of mph, as it feels better. You can laugh, but we all do it!

The main thing you should look for in a new bike, IMO is that it fits you. This will improve your comfort. If you're comfortable you'll be able to go faster. Drop handlebars will help with aerodynamics, but probably still less than wearing a less baggy jacket. The weight of the bike is likely to be negligible compared to the weight you've already lost, so don't blow the bank for the sake of a few pounds/grams.

If a road bike fits you properly and doesn't have the handlebars too low compared to the saddle, you ought to be able to get comfortable. That said you can still go pretty fast on a hybrid. Some of my personal records are set on my hybrid rather than my road bike, just because I happened to feel fitter the day I took the hybrid out.

So get a bike that fits and is comfortable. Obviously that means trying them out and making notes. If you are really serious you can go for an independent bike sizing/fitting or follow an online measurement guide rather than relying on the guy in the shop who will want to sell the bike in front of you.

If you're comfortable on your bike you'll enjoy riding and ride more often. This will make you faster. Have fun!