>>64059768
So I did a bit more digging. All the sites I saw in the top page of search engine results were in the rough ballpark of 0.03 mph and/or 0.048 km/h, which are equivalent if the converters I use aren't just outright lying to me. However, they didn't mention a source for their figures. The Wikipedia page for the common garden snail (Cornu_aspersum) suggests that the figure originally came from a 1974 edition of the Natural History magazine, which I can confirm (it's available online at https://digitallibrary.amnh.org/bitstreams/7b0fe60f-659e-49da-8821-c50f92c34d09/download - it's a bit ugly, but the list the figure comes from is on page 71 of the March edition, or page 309 of the pdf). However, the article also does not cite its sources, and I don't care enough to keep pulling at that particular thread.

Also, the Wikipedia article mentioned a newer source that suggested the top speed was closer to 2.4 m/h (Slugs and snails. Collins New Naturalist Library, Book 133, available for limited reading at https://books.google.com/books?id=pYT8CwAAQBAJ&pg=PT28#v=onepage&q&f=false - pic is the charts, no page numbers as there weren't any that I could see in the Google Books view but it does look like they're 15-20 pages into Chapter 1). That appears to be roughly accurate...for one entry regarding a different species of snail...on a large and rather inconsistent list...

tl;dr get me a grant and I can settle this once and for all because goddamn