It was a little trick but I got it working.The config file I am using is here
EDIT the URL to point to your website.Save it as stress.ubr.
NOTE:I am testing with 3 clients, so the stress will only start once we get 3 clients connected.
Download the Windows II6 ResourceKit from here then Execute:
C:Program FilesIIS ResourcesWCAT Controller>wcctl.exe -a 172.16.83.25 -z stress.ubr -l output.log
Now from the clients do(you can even open 3 from same server):
C:Program FilesIIS ResourcesWCAT Client>wcclient -v -d:16 172.16.83.25
Wait the 2 minutes and check the log file.
For me the most important was the Avg. Response time witch in my testes were really high.