This "full duplex" "2000 Mb/s" is just marketing confusion. Every modern gigabit NIC and switch will do this, and it's no big deal. Some manufacturers harping on bidirectional througput instead of one way throughput makes it confusing for those new to this. Newegg for example took it further with some switches being classified as 100/200/1000/2000 etc., as if they're different from switches advertised as 100/1000. But they're not, so it's just marketing confusion...
Teaming multiple NICs is an advanced topic, and to cut to the chase, will typically do
nothing for the home user in terms of single file transfer performance, even if he/she gets it set up properly with teaming software/drivers, a smart switch, a couple of computers with multiple NICs, fast storage arrays, etc. It can do something for multiple simultaneous transfers as seen on multi-user servers, but this situation is rare at home.
Here's more on that:
http://www.alacritech.com/html/teaming.html
Moreover, with 20 MB/s file transfer performance, you've already shown that your file transfer is not (at all likely to be) limited by network performance. So teaming / "2000 Mb/s" etc. would be pointless.
20 MB/s is not far from typical GbE performance for average / slow drives. The number I throw around is 30 MB/s, but this varies; some might get 20-25, some might get 40-45, etc., this depends mostly on the HDs involved, on both ends of the transfer, but of course depends on the entire chain, including the file system, state of the files on the drives (crowding, fragmentation), whether the HD controller and NIC are on a shared PCI bus, etc.
You can use tools like iperf to see what your network speed is in isolation of drive speed. These typically give figures much higher than file transfer speed, showing that the "problem" is not network per se.
E.g.
server: iperf -s
client: iperf -c
server -l 60000 -t 21 -i 3 -r
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