I've been using Hardkernel Odroid C2 for this reason. It looks a bit like a Pi but its Gigabit Ethernet can achieve near line rate, 930+ Mbps on iperf, see below for two Odroids connected across a gigabit ethernet switch.
# iperf3 -c 172.16.0.139
Connecting to host 172.16.0.139, port 5201
[ 4] local 172.16.0.142 port 49203 connected to 172.16.0.139 port 5201
[ ID] Interval Transfer Bandwidth Retr Cwnd
[ 4] 0.00-1.00 sec 110 MBytes 921 Mbits/sec 45 788 KBytes
[ 4] 1.00-2.00 sec 112 MBytes 937 Mbits/sec 0 878 KBytes
[ 4] 2.00-3.00 sec 112 MBytes 939 Mbits/sec 45 672 KBytes
[ 4] 3.00-4.00 sec 112 MBytes 938 Mbits/sec 0 717 KBytes
[ 4] 4.00-5.00 sec 112 MBytes 938 Mbits/sec 0 748 KBytes
[ 4] 5.00-6.00 sec 112 MBytes 939 Mbits/sec 0 765 KBytes
[ 4] 6.00-7.00 sec 112 MBytes 939 Mbits/sec 0 773 KBytes
[ 4] 7.00-8.00 sec 112 MBytes 939 Mbits/sec 0 775 KBytes
[ 4] 8.00-9.00 sec 112 MBytes 938 Mbits/sec 0 778 KBytes
[ 4] 9.00-10.00 sec 112 MBytes 938 Mbits/sec 0 779 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth Retr
[ 4] 0.00-10.00 sec 1.09 GBytes 937 Mbits/sec 90 sender
[ 4] 0.00-10.00 sec 1.09 GBytes 933 Mbits/sec receiver
iperf Done.