I'm not the most versed in editing graphic files, but I did try scaling your 500x500 pix ships down to 300x300pix at first with Gimp, then setting them in a shipImages folder for my theme. At least, those that needed scaling down (not all do). I didn't like what I saw. The images didn't appear as sharp. Now, that may have been me on a bad day, I don't know, but it was my impression.
What's that about 500x500 pics Grisha? I thought the modders should shift to 300x300 because it will look better now. Or am I mistaken? If I am that sucks big time :/