Curious to know if anyone knew of a tool or site I could load an image to and test it's "download speed" so I can figure out how to minimize wait time on a clients website?
I don't know such a service, but there are many monitoring websites, which you can analyze clients websites. These websites offers you details about objects loading speed e.g. images, scrips, css, html. Some sites can analyze each element [each photo, script, css/html file], but these services are paid services. Being my first post, I will not leave any link, but you can easily find such advanced services if you search 'website monitoring services' or other similar terms.
You can see image upload-time with photoshop. At fitur 'Save for Web' you can see upload time of an image.
Yeah, clean up the CSS and use a media query to feed high res images only to retina display-capable devices. That way you aren't force feeding high res graphics to devices that can't handle them.