At work, Tiemen Schut tested the performance under Linux for two Gigabit network cards, a D-Link DGE-550SX (optical) and an Intel Pro/1000 GT (standard Cat5e).
While the throughput is the same, the CPU usage is a major difference. Both Linux drivers allow setting some parameters for generating as little interrupts as possible. The difference:
CPU usage | Number of interrupts | |
Intel Pro/1000 GT | 30% | 5.000 |
D-Link DGE-550SX | 80% | 23.000 |
To recreate the test: