The rule of thumb wit TCP/IP networking is that it takes 1Hz of CPU power to process 1bps. So Ethernet at full speed takes 10Mhz of CPU power (20Mhz for full duplex), Fastethernet takes 100/200Mhz, Gigabit Ethernet 1/2GHz etc.
TOE takes this load from the cpu to a special ASIC (Appliction Specific Integrated Circuit) that does TCP/IP Processing in near wirespeed. Thus a servers CPU is left to do other work and only process higher layer traffic.