I have no clue for most of these questions, funny/sad.

I guess I have a KillerNIC, but I haven't even been using it for a year. I should get back to using it.

i would honestly say Fiber vs Cable, technically DSL is best @ least for online gaming such as UT99, so Fiber usually much less latency & cable companies dont usually promise guaranteed bandwith, just an approximation.
Depending on rest of machine, AMD only if your looking @ a higher clock i.e GHz or MHz, however a Good 3.6GHz P4 should be equivalent to a modern AMD,
so Intel preferred in my opinion, Nvidia vs AMD/ATi? Nvidia because their purchase of 3dfx and Voodoo is more closely integrated than AMD/ATi. NIC is dependent on Latency & MTU along with speed duplex settings, BigFoot Killer i believe is on Gigabyte motherboards standard @ least their gaming models, but Integrated (onboard) would probably have a higher preference and closer pathway straight to the center of the action so less physical latency, so to answer Onboard. In regards to a monitor (display) 120hz is going to bring your information back to you visually faster and feel more in sync generally than 60hz , your basically talking a flat panel TV for 120Hz without going insanely high price for computer display, but @ least that was the case last time i checked pricing. I will say tho when i play Unreal Tournament 3 for PC on my TV @ 120 it feels much more fluid than @ 60 on my desktop 1600x900 monitor. Side strafing for sure! keep your eyes on your opponent.