Mathey,
I just did something this morning where I needed to see a round circle and it saved the image quality. My part templates are set up for low or fast performance. Not sure if someone else may have a suggestion for you. Did you try saving the part immediatly after changing the quality? You might want to let us know what version of SW you're running and all the particulars as far as video card etc.
SolidWorks 2006 SP4.0
Windows XP Pro, Pentium4 3.00GHz
1.5 GB RAM, Matrox P650
Logitech Marble Mouse, CADMAN