Have you seen Killer NIC? For $279 it can seriously reduce latency and lag. It basically takes almost all of the networking load off of the CPU and handles the network buffers in its own memory, then uses optimized algorithms for common tasks. For example, instead of your OS having to traverse the whole networking stack to see if there's data on a port and then pull it, this thing does it in two quick instructions. That's helpful if you're polling a port all the time. Games have seen between 1 and 38 ms lower ping times, and performance gains up to 10% (slightly due to processor offload, but mainly due to not waiting so long checking and pulling data from a port).
It's mainly for gamers since latency is the killer for them, not raw bandwidth. But something like this should speed up a high-traffic business network -- VPN and remoting should love it. Is it cheaper to upgrade your whole network because your remoting UI is jerky, or to put these NICs in those systems that do remoting?
Yep, but you still can't get rid of the network latency which overruns all else. Try a program like pingplotter and see for yourself.