Instead of setting a size, you can make the information of size dissapear when you choose Full Size. It′s ridiculous when you say you want the full size image and they try to resize it.
Go to /wp-includes/media.php on line 84 and comment that line (//)
// any other type: use the real image and constrain it
// list( $width, $height ) = image_constrain_size_for_editor( $meta['width'], $meta['height'], $size );
This way instead of
<img src=”…” class=”…” width=”…” height=”…” />
you will get
<img src=”…” class=”…” />
=)
