Actually, I recently bought a PCMCIA adapter which is labelled as ST Lab Gigabit Ethernet (32-BIT) Cardbus Adapter. Unfortunately it doesn't work with FreeBSD even though FreeBSD does recognise it.FWIW, I have only ever seen 10 / 100 Mbps PCMCIA NICs. I don't think the PCMCIA bus is fast enough. And for usb, I think you are going to need USB3 if you want 1 Gbps performance (throughput) as opposed to 1 Gbps link speed...
iperf -s
iperf -c
Note that the raw data bandwidth of USB 2.0 is only 480Mbps.Interestingly I have just connected a 1Gb USB adapter to my laptop - a ThinkPad X61 - (it didn't work previously with other laptops) and it started working, so I guess my search is over.