The first image was mine 2 weeks after I bought it in 2014. This is after an hour of highway driving in an ice storm that hit San Antonio. I was also working on land oil rigs at the time so I understand what you are describing. Unless you can find a wide set of flaps that drops almost to the ground you will never completely get rid of some spray. I did find after installing step sliders that a lot of the middle stuff was mitigated by the sheet metal in the sliders. So you could reduce a considerable amount of the main stuff between the fenders by installing a wide-ish running board of some sort. I have seen some 4Runner packages with a wide flat running board/step bar installation. Not as durable as a slider but you sound like you're not looking for sliders as much right now. The 2nd image is with the sliders after a couple hours of wet trails but no deep mud. Just giving you something to consider.
