I somehow think "acceptable" dress is different from what you'll be comfortable in, and largely dependent on where (type of environment) you'll be in. One thing to be in the posher and/or more touristy parts of Jeddah, and another thing if, for example, passing through something like a bus terminal in a not-so-nice part. Just observations as a male who admittedly hasn't been to the KSA yet but have been in Egypt, Jordan, Malaysia (partially offset by a large minority of non-believers at least in urban areas) and Indonesia. What may be considered very modest dress in most of North America (unless one's in rural or suburban Utah) or Europe may be regarded as scantily-dressed in the more-conservative areas.