That said, yes, it's windy, as much of Argentina can be. So what tent to take kind of depends on whether you want to do some mountaineering, or more general backpacking. Because if you backpack and don't camp real high you should find some shelter from winds. In the high country, all bets are off.
Anyway, Sierra Designs' Orion AST ($219; www.sierradesigns.com) is actually a very tough little tent. Keep in mind it uses the same poles and materials as the Stretch Prelude you mention ($575), with the difference being the number of poles (three, versus four for the Prelude) and their configuration. Properly guyed out, and given a little shelter in the lee of a boulder or some trees, the Orion should be able to take just about anything it gets. Your big Prelude, of course, is made for this sort of thing, so it would shed the del Paine winds like a turtle.
One other interesting possibility would be Bibler's Lighthouse ($369; www.biblertents.com). It's a single-wall tent that uses Epic fabric, a very light, silicon-treated material made by Nextec. The Lighthouse is patterned after the Bibler Ahwahnee ($650), which is made with Bibler's traditional Gore Tex-like single-wall material. The Lighthouse, on the other hand, is absurdly light (just over three pounds) yet plenty rugged. It isn't billed as completely waterproof, but it'll keep you dry under several hours of hard rain—maybe more.
Otherwise, if I were shopping for a tent to take, I'd probably get something such as Marmot's Hypno ($349; www.marmot.com), a very sturdy and roomy three-season tent that weighs just under six pounds.
Whatever tent you do take, be sure to pack plenty of guylines. They make a huge difference in stabilizing a tent when it's windy.
Check out more of the year's best tents in Outside's 2004 Buyer's Guide.