I'm not sure I'd ever want to do distances like that on a bike that wasn't my own.
As far as the training bike goes, the best bike is one that you enjoy riding. You aren't going to enjoy riding as much if it doesn't fit you properly. (I speak with some experience in this regard.) So, first, determine if you need a WSD bike or not. (This is based on your relative proportions--you might need WSD if you have long legs and a short torso). You can start trying out bikes based on that. The number they gave you is a starting point. Ride lots of bikes, even the ones that you probably won't consider buying. Once you've got a couple that fit (and some that don't), you can go online and look up the geometry charts and compare them. That way, you can find out which features work for you and which don't. If you decide to get a second-hand bike (which can get you a lot more for your money), you can use this information to determine if a bike might fit. I'd still ask to test-ride it.
Your main consideration will obviously be the fit. This can be tweaked--new stem, new seatpost, new handlebars... Once you get a list of bikes that work for you, look at the frame material, components and gearing. Shimano 105 (or the equivalent) is a good place to start. As far as the frame material goes, that's an individual preference and it depends on how much you're willing to spend and the roads on which you'll be riding. Gearing...talking about that is not my area of expertise.
I'm sorry to have written a novel. If there's something I left out, I'm pretty sure someone will come along and add it. Happy shopping!
ETA: Go to a bunch of bike shops. Tell them what you want--a mid-range road bike. If they keep pushing the high-end stuff, leave. It means they want the sale more than finding a bike that works for you.