If you were referring to actual Ethernet using something like the HWIC-1GE-SFPs, a couple of points to note:
Q. Are there differences between the on-board Gigabit Ethernet ports and the HWIC-1GE-SFP?
A. Two copper Gigabit Ethernet ports are built into the Cisco 2821, 2851, and 3800 Integrated Service Router platforms. On the Cisco 3800 Series platform, an SFP Gigabit Ethernet port can be used instead of one of the copper Gigabit Ethernet ports. The feature set of the on-board Gigabit Ethernet ports and the HWIC-1GE-SFP is the same, except that Cisco EtherChannel® is not supported on the on-board Gigabit Ethernet interfaces
Q. What is the maximum throughput on the Gigabit Ethernet HWIC?
A. The HWIC bus interface is limited to 400 Mbps of full duplex. The actual throughput of the Gigabit Ethernet HWIC is limited by the throughput of individual platforms. Under bidirectional traffic of 1518 bytes or larger, the Gigabit Ethernet HWIC can support up to an aggregate of 350 Mbps on Cisco 2811 and 2821 routers, 400 Mbps on Cisco 2851 routers, and 500 Mbps on Cisco 3800 Series platforms.
ref: http://www.cisco.com/en/US/prod/collateral/routers/ps5854/prod_qas0900aecd80169bf0.html
For HWIC-1FE(2FE), you might also want to review: http://www.cisco.com/en/US/prod/collateral/routers/ps5854/prod_qas0900aecd80582015.html
