Not sure which of these you changed to change to "hiqh quality rendering in the viewport" but you can up the resolution of your texture itself to highest (be it image or standard checkerboard) in its hardware texturing attributes (attribute editor) as well as in the viewport itself going to shading > hardware texturing (option box). Turn off filtering and leave the top to 'multiply". This will result in the default checkerboard texture being very sharp. With an image, you'll want to play with the filters a touch as it may be too sharp and jagged.