In a gigabit network, you should enable jumbo frames and tweak the jumbo frame settings on your nic so that large files can transfer at greater speeds. In a packet of data, the header will remain the same but the payload size will increase. You should do this if you have gigabit switches and gigabit cards in place. Normally network cards will allow for tweaks of the Jumbo frame by several MTUs. With gigabit switches in place, the receiving switches may be 10/100 and the computer on the other end will not see a great benefit from this. However if you have cards in computers that are connected to a switch (1000 mbps/1 Gbps) and a NAS that supports Jumbo frames, the data transfer from these computers (normally a Server) will benefit from this tweak.
Ideally you would want your entire network on gigabit. In today’s economy, many if not most networks are a hybrid (a mixture of 1000 or 100 mbps) nodes (printers, computers, switches). There’s only one way to find out about performance. Transfer a large file (ISO or several megabytes) and time it slowly tweaking the MTU settings under the network card’s property.