Bzzzzt. You guys are all wrong. Zak was close back in reply 3, but his reply was missing a lot of information.
Wax alone will not help. If you use the wrong wax, you will go slower than if you had not applied any wax at all. The key to speed is choosing the right wax for the snow temperature. It is deep winter, so you should use a "hard" wax for cold snow temperatures. If it warms up, choose a softer wax.
Oh, and you'll never get it exactly right, unless you get lucky. Back when I was a lot more into skiing than I am now, I used to experiment with mixing different hardnesses to attain maximum speed. I got close, but it really is a science, and choosing the right wax is something that keeps the World Cup ski techs guessing. But close is good, and I spent many a ski-day as a speed freak--it was as if my skis had a mind of their own, and they wanted to go straight downhill as fast as possible.
Also, freshly waxed skis are almost always slow, unless you've done a really good job of scraping and polishing with cork. Otherwise it takes a few runs for the friction of skis running over snow to polish the bases.
Unfortunately, the only way you can have absolute control over the wax hardness is if you wax them yourself (as I used to do), but I guess you could request that they use racing wax instead of the all purpose stuff that the ski shops tend to use.