Getting back to the original question, from my experience doing exactly what he asked about (renting high performance skis instead of bringing your own) I have found a great variance in how well prepared demo skis are. I have had some so badly railed I could barely make it down one run, and others so nice I ended up buying that same brand and model when I got home.
My suggest is bring your own so you have something you are familiar and comfortable with, and then try some other skis at the base area so that if you take a run and don't like them you can bring them back for something else. I did exactly that at Winter Park a few years ago. The first pair (Volkls that were one of the more popular models at the time) were absolutely not to my taste, so I exchanged them after the first run. If I rented in town, it would have taken half the day to exchange them. The second pair I liked enough to do a second run, but traded them in for a thrid pair, which I kept the rest of the weekend.
I had an even worse experience at Big Sky. Whoever was in charge of keeping the skis tuned at that shop was totally incompetent as they all had heavy burrs on the edges. 3 pairs, 3 runs, I went back to my own skis.