The challenge with trying iperf is that I have to reconfigure some things to test it. I am currently router-behind-router with a twist.
The Motorola NVG589 in front of my pfSense system has a hybrid NAT as well as public IP, because I am paying for multiple IP addresses. So I have 5 IPs on the public subnet and then a private 192.x.x.x subnet. PFSense sits on one of the public IPs and I can use VIPs for the additional and NAT them in to a given host.
The issue is putting iperf out on one of those 192.x.x.x IP addresses, between pfSense and the AT&T router (actually sitting next to pfSense, but "outside" my firewall).
iperf can generate only 10's to 100Kbit/s in that situation, from inside my LAN to that immediate WAN before the AT&T router. I can get better iperf performance to a system I have at a colocation than a system sitting on my Motorola router just outside pfSense!
So to test my pfSense router I'd have to reconfigure it entirely, do the test, and then put it back so my family can get their internet back :)