It is claimed that Killer NIC is designed specifically for online gamers. It’s patented Lag and Latency Reduction (LLR) Technology gives you the competitive edge you need in the heat of battle. Or at least you can use the heat sink kill your opponent 
Killer NIC claims that performance of the Killer in online gaming kicks the ass. They measured performance on one identical machine with Killer and one without. FPS improvement for “World of WarCraft“ is 7.2% while Ping improvement is 31.5ms on average by the Killer over ordinary NIC.
This is possible because LLR delivers lower latencies and lightening fast connections by implementing a hardware-interrupt networking model. This means that when you fire at your opponent, you short will get there a split second faster giving you the edge over your competition. LLR also delivers smoother game-play by getting your network card out of the main game loop that draws the graphics bypassing the windows network stack means more FPS during online play, and better overall system performance while you game. [Link]
Others say about the Killer NIC
- Killer NIC — The Gaming Network Accelerator Card
- Bigfoot Networks Killer NIC Card Seen For The First Time
- Linux powers gaming “killer NIC”
