Powerstrip has a feature where you can resize your desktop while maintaining the same timings (they call it the custom resolution designer). I suggest you try it.
|Beginning with Build 480 of PowerStrip, a new, simple resolution "designer" is included that may ease the tedium involved in eliminating overscan. You would typically begin from the manufacturer's recommended but overscanned resolution and timing (e.g., 1280x720p), and, after ensuring the result is indeed sharp (albeit overscanned), you would access the designer from the PowerStrip custom resolution page (there's a little speedbutton above the Close button).|
1. PowerStrip menu > Display profiles > Configure
2. Switch to the manufacturer's recommended resolution
3. Click Advanced timing options
4. Center the image on the display using the position controls; TVs are designed to overscan, so do not try to adjust the screen size using the size controls
5. Click Custom resolutions
6. Click the "designer" speedbutton above the Close button
7. Size and position the designer window so that it stretches edge-to-edge, keeping in mind that the window will snap to values that the hardware can handle (e.g., the horizontal resolution will usually need to divisible by 8).
8. When you are done, click Ok to return to the Custom resolution dialog box and click "Add resolution", then follow the instructions on screen.
With any luck, the result will require only a tiny bit of fine-tuning in Advanced timing options.