Is there any option allowing to view the Preview Page in high quality mode like in the Full Page Editor? Even if this makes things a bit slower.
The way to get the best quality in the preview panel is to improve the quality of the thumbnail images.
Click on VIEW, Thumbnail Browser, Thumbnail Quality. Set that for HIGH.
That is maximum.
If you want high resolution, you can hover to the mouse over the thumbnail and click the space bar.
You could also set the slide show to IMAGES which will be high resolution.
Hope some of this helps.