I call bollocks!
The Killer NIC software that is running in the background would negate the improvement in offloading network processing onto the NIC.
So, we benefit by offloading the TCP stack, then bog the system down by running yet another program on the computer?
Most plug in NIC's these days feature the ability to offload some of the TCP processing onto the card, this is nothing new, indeed it has been a feature of all server oriented NIC's for many a year, or even decade.
To top it off, your test is based on a "finger in the water" method. You tested it on one day/time, then changed the card for the Killer card, and tried again. The situation was NOT exactly the same, you couldn't control the network congestion and routing once the packets leave your router, so its a purely speculative guess on the improvement at best.
So, lets call it the Killer Networks Placebo NIC shall we? It makes you feel better about being hopelessly outclassed by that guy with the big sword when you are grinding for XP.
Jobs because if he could have sold this as the iKiller, he could have made a bazillion dollars off of peoples gullibility on yet another device....