I was poking around on google scholar, reading about measurements of the vision of stomatopods and salticid spiders, and found some data.
This paper has some cool stuff about vision and pathfinding in salticid spiders (they are pretty good at looking at a prey item and then taking a complex indirect route that breaks visual contact to get into a position to strike, mentally computing where they are in relation to the target). It cites a visual acuity of 2.3 arcminute in the Anterior Medial Eyes (the big central ones, which have a double lens system making them a telephoto lens) of the salticid spider
Phiale. It also has some very cute diagrams of spiders, and is well worth a look.
This paper has some good information about stomatopod eyes, but is a lot harder to read. I think it says that
Oratosquilla scyllarus has a visual acuity of 8.4 arcminutes in the Acute Zone of the midband, but I'm not at all sure that they're talking about the same thing as the other paper, since they call it smallest usable ΔΦ
v. Just for reference, normal human visual acuity is around 5 arcminutes. If I'm interpereting these papers correctly, jumping spiders have a fair bit better visual acuity than mantis shrimp. I also found some cool data about accuracy of depth perception in both salticids and stomatopods, but I haven't yet figured out how to interpret the numbers given.
Interestingly, both stomatopods and salticid spiders have some unusual visual habits, where when they're examining an object to identify it, they scan their eyes back and forth across it, and also rotate their eyes. Normal creatures only do scanning type movements when they are following a moving object, and use saccadic (jerky) movements for that sort of examination. In the spider paper there's an adorable diagram at the bottom of page 8, showing a jumping spider leaning back and forth to scan back and forth get a good look at something (their eyes are moveable, but not to nearly the degree of stomatopod eyestalks, and they use body movements to do most of their looking).