A little introduction about myself. I work for a networking company (unfortunately I cannot give you the name). We make network controller IC for both server and desktop platform.
I have been reading a number of posts and I hope I can clarify a number of things for everyone here.
Jumbo frames was invented by Alteon back in the days of 10/100Mbit Ethernet. At the time, it was felt that an increase in the MTU size (from maximum of 1518 to 9K) would be of great benefits in data transfer.
I have been in this industry for 9 years and along with my colleages we all agree on one thing: Jumbo frames is a curse. It forces everything connecting to it support it, otherwise things don't work. Even to this day everything we built we have to support it even in environment that don't uses it.
So to clarify for a number of people. If you truly want to use Jumbo Frames, everything connected to it must support Jumbo Frames. Otherwise, once data is initiated, the data stream would automatically adjust the MTU size and finally the MTU got set back to 1518 anyway.
But I digress. Here is my current setup. Netgear Gigabit Ethernet Switch connected to 2 computers. One computer is using a Gigabit Ethernet Card made by Netgear, with a Realtek chip. The other computer is using Intel Gigabit LOM (Lan on Motherboard). The data transfer rate (copying large DVD files) varies between 190Mbit to 250Mbit. CPU utilization is around 30%.
The MTU size is from 1400 to 1518.