I definitely did something wrong here.
dogfood:~$ iperf -s -l 1m -w 4m -m
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 8.00 MByte (WARNING: requested 4.00 MByte)
------------------------------------------------------------
[ 4] local 172.26.196.49 port 5001 connected with 172.26.197.120 port 50595
[ 5] local 172.26.196.49 port 5001 connected with 172.26.197.120 port 50596
[ ID] Interval Transfer Bandwidth
[ 4] 0.0-10.0 sec 676 MBytes 564 Mbits/sec
[ 4] MSS size 8961 bytes (MTU 9001 bytes, unknown interface)
[ 5] 0.0-12.4 sec 127 MBytes 85.6 Mbits/sec
[ 5] MSS size 8961 bytes (MTU 9001 bytes, unknown interface)
[SUM] 0.0-12.4 sec 802 MBytes 542 Mbits/sec
[ 6] local 172.26.196.49 port 5001 connected with 172.26.197.120 port 50597
[ 4] local 172.26.196.49 port 5001 connected with 172.26.197.120 port 50598
[ 6] 0.0- 0.4 sec 9.47 MBytes 222 Mbits/sec
[ 6] MSS size 8961 bytes (MTU 9001 bytes, unknown interface)
[ 5] local 172.26.196.49 port 5001 connected with 172.26.197.120 port 50599
[ 4] 0.0- 0.4 sec 13.9 MBytes 264 Mbits/sec
[ 4] MSS size 8961 bytes (MTU 9001 bytes, unknown interface)
[ 5] 0.0- 1.1 sec 35.6 MBytes 266 Mbits/sec
[ 5] MSS size 8961 bytes (MTU 9001 bytes, unknown interface)
[ 6] local 172.26.196.49 port 5001 connected with 172.26.197.120 port 50600
[ 6] 0.0- 1.3 sec 9.62 MBytes 62.1 Mbits/sec
[ 6] MSS size 8961 bytes (MTU 9001 bytes, unknown interface)
[SUM] 0.0- 1.3 sec 68.6 MBytes 442 Mbits/sec
[ 4] local 172.26.196.49 port 5001 connected with 172.26.197.120 port 50601
[ 4] 0.0- 0.1 sec 8.25 MBytes 481 Mbits/sec
[ 4] MSS size 8961 bytes (MTU 9001 bytes, unknown interface)
[ 5] local 172.26.196.49 port 5001 connected with 172.26.197.120 port 50602
[ 5] 0.0- 0.1 sec 7.00 MBytes 448 Mbits/sec
[ 5] MSS size 8961 bytes (MTU 9001 bytes, unknown interface)
[ 6] local 172.26.196.49 port 5001 connected with 172.26.197.120 port 50603
[ 4] local 172.26.196.49 port 5001 connected with 172.26.197.120 port 50604
[ 6] 0.0- 0.2 sec 9.75 MBytes 445 Mbits/sec
[ 6] MSS size 8961 bytes (MTU 9001 bytes, unknown interface)
[ 4] 0.0- 0.3 sec 6.12 MBytes 175 Mbits/sec
[ 4] MSS size 8961 bytes (MTU 9001 bytes, unknown interface)
[SUM] 0.0- 0.3 sec 15.9 MBytes 452 Mbits/sec
[ 5] local 172.26.196.49 port 5001 connected with 172.26.197.120 port 50605
[ 4] local 172.26.196.49 port 5001 connected with 172.26.197.120 port 50606
[ 5] 0.0-10.2 sec 680 MBytes 560 Mbits/sec
[ 5] MSS size 8961 bytes (MTU 9001 bytes, unknown interface)
[ 6] local 172.26.196.49 port 5001 connected with 172.26.197.120 port 50607
[ 4] 0.0-20.2 sec 533 MBytes 221 Mbits/sec
[ 4] MSS size 8961 bytes (MTU 9001 bytes, unknown interface)
[ 5] local 172.26.196.49 port 5001 connected with 172.26.197.120 port 50609
[ 6] 0.0-30.3 sec 532 MBytes 147 Mbits/sec
[ 6] MSS size 8961 bytes (MTU 9001 bytes, unknown interface)
[ 4] local 172.26.196.49 port 5001 connected with 172.26.197.120 port 50610
[ 5] 0.0-40.3 sec 534 MBytes 111 Mbits/sec
[ 5] MSS size 8961 bytes (MTU 9001 bytes, unknown interface)
[ 6] local 172.26.196.49 port 5001 connected with 172.26.197.120 port 50611
[ 4] 0.0-50.4 sec 533 MBytes 88.8 Mbits/sec
[ 4] MSS size 8961 bytes (MTU 9001 bytes, unknown interface)
[ 5] local 172.26.196.49 port 5001 connected with 172.26.197.120 port 50612
[ 6] 0.0-60.4 sec 530 MBytes 73.5 Mbits/sec
[ 6] MSS size 8961 bytes (MTU 9001 bytes, unknown interface)
[ 4] local 172.26.196.49 port 5001 connected with 172.26.197.120 port 50613
[ 5] 0.0-70.5 sec 533 MBytes 63.4 Mbits/sec
[ 5] MSS size 8961 bytes (MTU 9001 bytes, unknown interface)
[ 6] local 172.26.196.49 port 5001 connected with 172.26.197.120 port 50614
[ 4] 0.0-80.5 sec 534 MBytes 55.7 Mbits/sec
[ 4] MSS size 8961 bytes (MTU 9001 bytes, unknown interface)
[ 5] local 172.26.196.49 port 5001 connected with 172.26.197.120 port 50616
[ 6] 0.0-90.5 sec 530 MBytes 49.2 Mbits/sec
[ 6] MSS size 8961 bytes (MTU 9001 bytes, unknown interface)
[ 5] 0.0-303.8 sec 7.50 MBytes 207 Kbits/sec
[ 5] MSS size 8961 bytes (MTU 9001 bytes, unknown interface)
[SUM] 0.0-303.8 sec 4.83 GBytes 137 Mbits/sec