Oui mais tu m'as dit toi même que sous Windows, ... Rwin ... et qu'il fallait donc ouvrir plusieurs connexions en parallèle pour avoir le débit réel maxi.
Voila ce que ca donne avec ta dernière commande (c'est celle que j'utilisais avant) et avec la même en rajoutant le paramètre -w 500k.
C:\iperf>iperf -c 3.testdebit.info -i 2 -t 20 -r
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 64.0 KByte (default)
------------------------------------------------------------
------------------------------------------------------------
Client connecting to testdebit.info, TCP port 5001
TCP window size: 64.0 KByte (default)
------------------------------------------------------------
[ 4] local 127.0.0.1 port 49663 connected with 89.84.127.55 port 5001
[ ID] Interval Transfer Bandwidth
[ 4] 0.0- 2.0 sec 7.88 MBytes 33.0 Mbits/sec
[ 4] 2.0- 4.0 sec 7.88 MBytes 33.0 Mbits/sec
[ 4] 4.0- 6.0 sec 7.75 MBytes 32.5 Mbits/sec
[ 4] 6.0- 8.0 sec 8.00 MBytes 33.6 Mbits/sec
[ 4] 8.0-10.0 sec 8.12 MBytes 34.1 Mbits/sec
[ 4] 10.0-12.0 sec 8.00 MBytes 33.6 Mbits/sec
[ 4] 12.0-14.0 sec 8.00 MBytes 33.6 Mbits/sec
[ 4] 14.0-16.0 sec 8.00 MBytes 33.6 Mbits/sec
[ 4] 16.0-18.0 sec 8.00 MBytes 33.6 Mbits/sec
[ 4] 18.0-20.0 sec 8.12 MBytes 34.1 Mbits/sec
[ 4] 0.0-20.1 sec 79.9 MBytes 33.4 Mbits/sec
[ 4] local 192.168.1.10 port 5001 connected with 89.84.127.55 port 42754
[ 4] 0.0- 2.0 sec 8.25 MBytes 34.6 Mbits/sec
[ 4] 2.0- 4.0 sec 8.44 MBytes 35.4 Mbits/sec
[ 4] 4.0- 6.0 sec 8.38 MBytes 35.2 Mbits/sec
[ 4] 6.0- 8.0 sec 8.38 MBytes 35.2 Mbits/sec
[ 4] 8.0-10.0 sec 8.38 MBytes 35.2 Mbits/sec
[ 4] 10.0-12.0 sec 8.42 MBytes 35.3 Mbits/sec
[ 4] 12.0-14.0 sec 8.40 MBytes 35.2 Mbits/sec
[ 4] 14.0-16.0 sec 8.38 MBytes 35.2 Mbits/sec
[ 4] 16.0-18.0 sec 8.40 MBytes 35.2 Mbits/sec
[ 4] 18.0-20.0 sec 8.39 MBytes 35.2 Mbits/sec
[ 4] 0.0-20.1 sec 84.2 MBytes 35.2 Mbits/sec
C:\iperf>iperf -c 3.testdebit.info -i 2 -t 20 -r -w 500k
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 500 KByte
------------------------------------------------------------
------------------------------------------------------------
Client connecting to testdebit.info, TCP port 5001
TCP window size: 500 KByte
------------------------------------------------------------
[ 4] local 127.0.0.1 port 49670 connected with 89.84.127.55 port 5001
[ ID] Interval Transfer Bandwidth
[ 4] 0.0- 2.0 sec 8.00 MBytes 33.6 Mbits/sec
[ 4] 2.0- 4.0 sec 7.50 MBytes 31.5 Mbits/sec
[ 4] 4.0- 6.0 sec 7.50 MBytes 31.5 Mbits/sec
[ 4] 6.0- 8.0 sec 7.00 MBytes 29.4 Mbits/sec
[ 4] 8.0-10.0 sec 7.50 MBytes 31.5 Mbits/sec
[ 4] 10.0-12.0 sec 7.50 MBytes 31.5 Mbits/sec
[ 4] 12.0-14.0 sec 8.00 MBytes 33.6 Mbits/sec
[ 4] 14.0-16.0 sec 7.75 MBytes 32.5 Mbits/sec
[ 4] 16.0-18.0 sec 6.88 MBytes 28.8 Mbits/sec
[ 4] 18.0-20.0 sec 7.62 MBytes 32.0 Mbits/sec
[ 4] 0.0-20.0 sec 75.4 MBytes 31.5 Mbits/sec
[ 4] local 192.168.1.10 port 5001 connected with 89.84.127.55 port 42756
[ 4] 0.0- 2.0 sec 17.2 MBytes 72.2 Mbits/sec
[ 4] 2.0- 4.0 sec 20.2 MBytes 84.7 Mbits/sec
[ 4] 4.0- 6.0 sec 22.4 MBytes 93.8 Mbits/sec
[ 4] 6.0- 8.0 sec 20.7 MBytes 86.7 Mbits/sec
[ 4] 8.0-10.0 sec 16.7 MBytes 69.9 Mbits/sec
[ 4] 10.0-12.0 sec 20.1 MBytes 84.1 Mbits/sec
[ 4] 12.0-14.0 sec 21.0 MBytes 87.9 Mbits/sec
[ 4] 14.0-16.0 sec 21.7 MBytes 91.2 Mbits/sec
[ 4] 16.0-18.0 sec 21.4 MBytes 89.8 Mbits/sec
[ 4] 18.0-20.0 sec 15.7 MBytes 65.9 Mbits/sec
[ 4] 0.0-20.0 sec 197 MBytes 82.6 Mbits/sec
C:\iperf>