The ST50 should have a pixel by pixel or 1 to 1 pixel setting that turns off overscan. If it does and you turn this on that will turn off the sets video processing for scaling etc letting the 103 do that if the 103 is set to output 1080p. You can also use the 103's other picture enhancement features to see if you can fix the sharpness etc. issues.
I couldn't find that feature anywhere in my picture settings menu. Will it make any difference if I don't have that or any other way to turn off my sets processing?