I second Matt's reply. I have owned/flown the Switchblades and Vectors. The SB size for size has more power, goes upwind a little better (but the Vector is no slouch), and better hangtime. The Vector relaunches much better, pivot turns faster (although it isn't what I'd call a fast turning kite, but that's why I like in smaller sizes - don't want a kite that's too zippy), actually boosts quite nicely, average power compared to other kites I've flown, and is just a nice stable well behaved kite. It's not just for beginners. I like it in nine meters on down, but it's a great kite in any size.
If you can, demo the two kites (the Z and Vector). That's the best way to decide. It's a personal thing, like trying on shoes. Some will "feel" better than others.
Everyone has their favorites and I'd like to share mine...While your at it, try the Airush Lithium. As much as I liked the Vector, the Lithium I tried on for size felt "ahhh!" just right. More power, turns quicker, same bar pressure, shorter depower throw (great if you have short arms), same easy relaunch, same range on the top end and much better on the bottom end. The adjustable (Smart Bar) bar is pretty cool too; one bar for all of your kites in the line. It has just a little less upwind ability of the Vector, a subtle distinction, but it's not an issue (and the Switchblade, like other high aspect designs, are upwind machines). I get to where I need to go without a second thought.
The only challenge is price. Chances are the Vector and the Slingshot Z have closeouts that are hard to beat. I'm betting you're going to be happy with nearly any kite out there. Different designs always involve compromise, and there will be somethings you like about each. Enjoy!