Fast Ethernet is 100Mb/s throughput
12 MB/s speed (theorhetical)
Gig Ethernet is 1000Mb/s throughput
125 MB/s speed (theorhetical)
10 Gig Ethernet is 10,000Mb/s throughput
1250 MB/s speed (theorhetical)
Pratically on ISCSI 10 Gig the throughput is 300-500 MBps it is very good.