To be honest, I would think you would be wasting time and money doing all that swapping for little gain. I don't know much about the Podium, but the Trek is their most basic option, and really doesn't warrant upgrading. Not to say that either is a bad bike, both are good, but the money you would using for the upgrade would be better spent on things such as good bibs, jerseys, flat kit, gloves, shoes, pedals, etc.

Personally, I would go one of two ways. You could save for the bike you really want (the Allez). If that would take too long, then I would go for the Trek. That way you have more money for the necessities I mentioned, and if you get another bike in 6 months you won't feel like you have sunk money into your current ride. I would not buy any of these bike with the intention of selling them. In my area, bikes like these do not sell very well on the 2nd hand market.

Being a beginner, I would try to find a good shop that will listen to your needs and be willing to help. It seems rather clear you do not know what size you are, and don't know which bike is most comfortable for you. That can be a bad combo when looking for a second hand bike. The $850 you plan to spend on those two bikes should easily get you an entry level road bike at an LBS that you know is comfortable, fits, and has a warranty. Plus if it is a good shop, you could end up with a bunch of new riding buddies!