Remember that the LEDs are just used for backlights, rather than the fluorescent tubes used in other monitors. Some manufacturers play tricks with the LEDs to extend the dynamic range of the display, but that sounds more than a little bogus to me.
If you're really concerned about the response time of the monitor, get a 120Hz model with a 2ms gray-to-gray response. It will probably be a TN panel, inferior to the S-PVA Dell for everything but fast-twitch gaming, and it'll be a lot more expensive.
Some hardcore gamers want high refresh rate CRTs. They probably are frying their ears listening to vinyl records played through vacuum tube power amps. Having to drop out of the game every 20 minutes to flip LPs must be a drag, though.