The squeak is belt slip at higher rpms. That manual tensioner will always cause a little belt slip at high rpms due to belt expansion. I would run the stock tensioner, the one that came with the car....Try a 68.5" belt that may work with your setup...I am not certain though so just get a 6 rib one and test it out.
http://www.5150rsx.com/images/belt_test.wmv
Watch when they lot off the gas at high rpms how much the stock tensioner goes bak to its original location.
Run it like this but include the A/C.
