I agree with Ron, on both counts. Demo if you can, but it might be hard to find Head and Fischer demos. I ended up narrowing it down to those two, but couldn't find any to demo (each had demo days in my area that had already passed, and no shops that I could find had demos of the ones I wanted to try). I ended up buying the Heads without demo'ing and got lucky, but if you plan ahead and contact the companies directly or their reps (maybe Rusty can tell you who to get in touch with in your area for the Fischers?) they might be able to tell you when and where they'll have demos in your area. The nice thing about this is that you can often ski several different skis within a single line (e.g., Fischer RX6 and RX8, Head iC 160, iC 180, etc.).
In addition to reviews on this site (search the gear reviews forum for each of the skis you're considering), Peter Keelty has good reviews of skis that might be useful. It might be worth the price of subscription. http://www.realskiers.com/