I think the first thing to consider is your current bike and why you want to move on. That's not to say there isn't anything wrong with going to a flat bar bike, but if your current bike is 'fixable', you could save yourself some cash. The 'fit' of a bike is very important and simple things like moving the seat or bars can make a big difference ... and, of course, it could just be that your current bike isn't right for you (let's not overlook the obvious eh?).
Firstly, what is your current bike and what is it about it that makes it uncomfortable?
To give you some idea of how things can be changed, read my story on the
Sow's Ear. That's extreme and doesn't change the fact that I started with a cheap bike that was too small for me, but that bike now serves as the tow vehicle for my daughter's tag-along bike and was hated and unusesd before that. Some of the changes may be applicable to you (like seat position, the stem extension and the longer seat post).
Another thread to peruse is this one on
seat height. The relevant post is the second one where I describe how to set up your seat and what to look for in handle bar position.
There are plenty of other threads talking about this stuff here - those were just two that occured to me as I typed.
I urge you to look closely at your current bike's setup before buying a new bike. There are two reasons for this. Firstly, setting her up properly may solve your problems (saving the expense of a new bike). But even if it doesn't, it will give you a better idea of what you like and dislike than you have now and so is worth the effort. It'll also give you a bit more experience with which to judge the shop you're dealing with - some shops are good and some are sharks, often it's hard to tell the difference until after you've been burnt.
Now, to the bikes you're looking at. I can't offer definitive opinions because I don't know those bikes. Generally though, when buying from the same manufacturer, you get what you pay for when you go up from one model to the next. Buy the best you can afford. The differences in components can be in efficiency, weight, durability, and aren't always obvious. However, look at lots of other brands too, just to make sure you're on the right path. It's confusing but that confusion fades the more you do it.
Have fun and keep asking questions
Richard