The best thing to do is go for a test ride. Just out of curiosity, is there any particular reason you decided to go with REI and not a bike shop? You can sometimes get pretty good deals on closeouts, the service you'll get is far better if the shop is decent, and you're much more likely to have a bike that's properly fitted and adjusted for you.

For the type of riding you're planning on doing, you could ride pretty much anything, and many people are perfectly happy with sora (and frankly, components won't make much practical difference to you at this point). However, if you buy the Speedster, don't plan on upgrading it -- that would be very cost inefficient and your results won't be as good. Rather ride it until you know what you really want, sell it, and buy something better.