EPS, is an acronym for Encapsulated Post Script - it is a package of information (vector and raster elements) used for cross-platform print documents.  Most would considered this a legacy format, well supported for print. In terms of vector information - it is probably the best choice for what you describe, Willow. 

The EPS format can be used for RGB images - but in fact EPS will never be efficient for rgb, as it is designed for post-script print files.

Your vector images will always be printable as EPS, but it's not a particularly efficient file format and if you do include raster images, the transparency is not well accomodated (as you may have to save the alpha channel separately)

There should be a go-to summary of file formats and their strengths and weaknesses.
For example, you are incorrect about PSD files and resizing. All raster images will pixelate when enlarged.

Is a Photoshop EPS file a vector format?
I have a pretty tight design that has a fixed width. However, when editing a Web Part, the dialog gets cut off or sometimes doesn't get display at all because of the frame's overflow.

I would like to implement a floating Web Part properties dialog. Any suggestions on how to approach this and apply it across my site collection?
