Killer NICs were an interesting curiosity. They employed a Linux stack on the chip so that it could handle all the work of rearranging and handling packets and ping without the need for CPU intervention.
There were some minor benefits if your PC tended to be network heavy (Stream and play for example) But it really doesn't solve the problem of the edge (router/gateway) having enough bandwidth. With today's household families using multiple gaming and streaming devices at once, this makes killer kind of moot.
I would prefer a good Router like untangle, or DUMA OS (high end netgear), or pfSense. The first and last my preference because installing 10gb NICs intel NICs is easy.