The answer is the one hope for, I suspect...
My LAN comprises two segments, one is 100Mbps, the other is gigabit. It comprises a Netgear gigabit switch with various equipment connected to it, one of which is the Netgear router, which operates at just 100 Mbps. There is stuff connected to both segments, gigabit and 10/100. So far as the gigabit switch is concerned, it will see the router as just another device, connected at 100Mbps.
When transferring large volumes of data, between systems connected directly to gigabit, I certainly see actual speeds of 150-300 Mbps, therefore it does get the benefit of gigabit (albeit limited by disk access speed and other bottlenecks).
At risk of alienating the Linux community, I actually find Windows' task manager the best of the bunch for showing network performance, the graphs and percentages are easy to interpret and, if you decide to check with a stopwatch, turn out to be quite accurate too.