Dynafit is definitely the way to go, but your boots need to be compatible. It is unusual to see them for sale, used, but the TLT Speed does run a bit cheaper than other AT bindings. BD sells boot soles with Dynafit inserts that you can swap out on their new Factor and Method boots.
I have 175 VooDoos that are great for touring, but they come up a bit short at higher speeds and larger radius turns. (Same mold as the Havoc just a lighter lay-up.) The 175 Kilowatt might be a better option as a quiver of one. I wouldn't recommend going up to a 185 in the Kilowatt unless you are pretty aggressive and have the weight to work the ski. If you like a longer ski the 185 Voodoo/Havoc would be a good choice. You could step it up a notch and get some 180 Verdicts to grow into, as well. I end up skiing my first generation Verdicts most of the time. I'm 5' 10" and 175 lbs. Here's another take on the BD line-up from a sponsored athlete's 1/1/09 blog: http://www.tetonat.com/
You can demo all these and more from BD Retail. They generally put Fritshi's on them which will accept most any boot. You can also put a couple of the rentals toward your purchase. Call ahead to reserve the gear. They will also wax and mount the skis for you if you spend a minimum of around $300.