The skis the World Cup racers ski on are hand built to their exact individual specifications and preferences. Then they start the season with a bunch of pairs that they test and retest, tune and retune, until they finally select just a pair or two that become their primary race skis. Sometimes skis "like" theirs are available, if you have the right connections, although they still won't be built specifically for you. Typically these skis won't look like much--simple laminated square sidewall construction, with no ridges, bumps or baubles on their top skins. Cosmetically, they may have the same graphics as the retail skis, but their construction may or may not even resemble what's available on the retail racks.
But don't overlook the retail skis. Some manufacturers--Fischer included--do offer excellent square sidewall hand-built race skis to the public. If you can demonstrate a need for more ski than that ... they'll know it, and they'll give them to you!
Also keep in mind that these very high end skis are NOT necessarily better for most skiers. They are high-strung, demanding, and unforgiving. They need to be tuned precisely and waxed carefully and often. The very best skiers can get the most out of them, but they are too much ski for most skiers. If you aren't up to the ski, it will be slower than a more forgiving model.
Finally, real World Cup stock skis may not last very long. They aren't built for durability or longevity. They're built for performance. Among other things, they typically have very narrow edges that are easily damaged and won't hold up to many tunes. You could go through a VERY expensive pair of skis very quickly!
As far as length goes, what do you intend to do with them? If you want them for fun, or for "informal" racing, get whatever length you like. Shorter is better, for slalom racing (but read the warning in the next paragraph), and World Cup racers typically go as short as the rules will allow. If you aren't skiing official FIS races, there are no rules.
If you need "FIS-legal" skis, remember that the new rules this season specify a minimum of 165cm for men. That's 10 cm longer than most of them used last season. But also remember that there is a reason for these minimum length rules: Safety! Short race slalom skis can carve such tight radius turns, and their grip is so tenacious, that they can easily subject a good skier to forces that will hurt you. And shorter skis are less forgiving of error, too. Like a thoroughbred race horse, one little mistake and they'll throw you--hard.