Question : Network configuration for fastest possible speed

I have two "experts" telling me conflicting facts.  The first expert says the locking down a NIC and switch port to 100 full duplex will make the network go as fast as possible.  The other expert says that he has seen better network speed with leaving both ends set to auto negotiate.  

Personally to me it seems that 100 FD would give the fastest performance because the devices would not have to “talk” about the speed and duplex rate, but I didn’t want to go through the lengthy process to prove the facts.  If anyone has any first hand experience with this question, please include the type of devices you have seen this scenario tested on.

Thank you for your time.

Answer : Network configuration for fastest possible speed

Manual is the best way to guarantee maximum throughput.  I have seen autonegotiation devices drop to Half duplex under heavy load because the device was too busy to send the control packets.
Also keep in mind that Autonegotiation is designed to work only if BOTH devices are set to auto.  Otherwise, you will likely end up with 100 Mbps Half duplex on most of today's devices.

Virtually every switch vendor out there recommends locking down speed and duplex except in 2 instances:
 - Gigabit.  The autonegotiation also includes flow control so is needed.
 - "Guest" ports.  If you don't know that the same device is always coming back to the same port, you *may* want to set it to autonegotiate.

Some people have complained that this means the end users now have to manually configure their PC's to manual 100/FD, but if you maintain that as a standard, you never need to worry, even if they move.