Jim Thompson:

I tried printing to PDF at 600dpi... looks crappy unless you zoom in.

It has to, since the "standard" monitor resolution is 75 DPI.

If you have a monitor 15" wide with a resolution of 1280 pixel, your screen
resolution is 85,33 pixel per inch.

You can use software tricks to reduce the "pixelation" of the image by
smoothing the border between one pixel and the next, but the resolution
will remain the same.

Or you can print it 1:1, but the dimension of the printout will be about
1/10 of the screen.