How/where to change the default size of inline images? For the life of me, I can't seem to figure out how/where to change the default size of inline images (that is, images that have been inserted into the body by way of the wysiwyg editor's Insert/Edit Image button). It's likely that I'm missing something obvious here as I've only had one cup of coffee today... tragic, I know.
I would use the Image Resize Filter or Image Autosize Filter modules. These module add a filter to your input format that automatically resizes images added through the WYSIWYG editor. Image Autosize Filter allows you to set a maximum width, which seems like it would work for your case.

As a precautionary measure, you could add some CSS like this as well:

.node img {
    max-width: 450px !important;
    height: auto !important;
    border:0px;
    margin:0em;
}