Welcome to the Quilting Board!
I do not know if this has been mentioned but the format of the image also makes a big difference. PNG formats have much larger files than a jpg. Reason is PNG are for editing so things are not merged together. jpg is merged into a single layer so they are smaller. I have a recipe program that I failed to notice the default setting was PNG so every recipe took twice the memory on my computer. Once converted to jpg everything was lightning fast for loading. You can keep your original as PNG but save another copy a jpg and it will speed things up.
I hear ya.... the elusive 1/4 seam still evades me too!
Mother yourself just as you would your own children, you will be surprised how much better you feel...Debbie Marie