I have my iMac hooked up to my led tv via mini display port to hdmi.

I am using mirror mode but my desktop on my tv is too big with overscan on and it cuts off the menu bar on the top to where i can't see it, but there is a 1inch bar of black around the tv if i turn it off. None of the other modes seem to quite work . And i cannot switch to the 120hz refresh that my tv can play there is not an option.

Is there anyway to custom scan to fit screen?
Also is there a way to completely turn off the iMac display, I'm using sleep time but screen still is on but dim and black.