Are you going to order the stem online, or buy it at a local bike shop ( LBS )? My bike came from an LBS in my neighborhood, but the fit wasn't quite right. I've been experimenting, and they've let me bring my stem back and exchange it for another one a few times until I got exactly the right length, angle, and all that. If you can find a shop that will do the same for you, it'll be easier and less expensive, if you don't get it right the first time.

Here's what a +17 looks like





Turns out my shoulders were getting sore because the bars were too high, not too low. After lots of fidgeting around, I replaced this with a -6, which looks like this





I shouldn't admit to something so Fredly as having run a +17. People will make fun of me for it. Anyway, you won't be able to pick the right fit from seeing pictures of other peoples' bikes, but I'm hoping this will give you a better idea of the difference between +/- 6 and +/- 17, since you asked.