When scaling a panel, the result becomes very pixelated. Try turning on the nofilter flag for a model and look at it. You can easily see pixelation effects. The same happens with panels. Stretch a panel to 4x on each side, you simulate the exact effect when zooming in on an image in a graphics edittor (like MSPaint or the GIMP). Scaling to 2x should be the very highest you should go and 2x is only decent for when using a very high resolution where the pixels on the monitor are very small.