Disable loopback interface lo0 on 10.8.4?
The version of iperf I have (from Homebrew) does indeed allow binding the client and server to different interfaces, like so:

iperf -s --bind 10.0.0.1
iperf -c 10.0.0.1 --bind 10.0.0.2


(for the purpose of this answer I assume that you want the server on .1 and the client on .2)

The problem is that the routing table (visible through netstat -rn) appears to override this, sending traffic to 10.0.0.1 through the loopback interface.

Rather than disabling loopback altogether, you can delete that specific route:

sudo route delete 10.0.0.1 127.0.0.1


I found that this caused my Mac to be unable to reach itself (on that IP) for a few seconds, until it found an alternate route out the other interface and through my router. Once that route showed up in netstat -rn, iperf worked fine. Here's my before and after:

[  4] local 192.168.2.99 port 5001 connected with 192.168.2.101 port 5001
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.0 sec  16.7 GBytes  14.3 Gbits/sec


And after:

[  4] local 192.168.2.99 port 5001 connected with 192.168.2.101 port 5001
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.0 sec   343 MBytes   288 Mbits/sec


288Mbps being a fairly reasonable speed considering that one of the interfaces in use is 802.11n wireless.

I was also able to return my routing table to normal by simply toggling the interface off and on again.