Different abilities. The lpx is corsair midline series, performance is mediocre, speeds and timings are mediocre. Corsair does have worse, the Elite series and better the Dominators. The Doms are technically faster, lower Cas, better timings and will handle an OC much better than the Vengeance series. But cost more.
Personally, I'm partial to the G-skill Trident-Z RGB vrs the Dominators, same abilities, lower price, customizable leds.