I finally scored a PS/2 Intellimouse 1.3A from The Stack(R). This one appears to have seen a fair bit of use and is crying out for a Retr0brite job, but after a little cleanup it's working just fine. About 10 years old by the looks of it, possibly acquired with P4/SDRAM machines (the last ones of which have been retired from active service recently). Datasheet says 400 ppi, and in fact it runs about as fast as my 400dpi opticals (if obviously a bit less smoothly). Last datasheet revision was in 2006... so those must have been among the last mechanicals sold.
Now that's a bit of a different grip compared to the Intellimouse Optical 1.1A or the Logitech M-BJ69. Compared to those, your hand sits a bit further back, and your fingertips are approximately in the middle of the keys rather than near the front edge. Clicks require a bit more force than on those newer rodents (less leverage). However, using the scroll wheel is a breeze. It has fewer clicks per revolution, but turns very lightly and never requires any contortions whatsoever. By contrast, the wheel on the Intelli Optical 1.1A seems impossibly high at times (partly because it does in fact rise above the keys a fair bit more, no doubt).
It appears that when the fingertips moved to the front edge, they forgot to shift the scroll wheel as well... or more likely, it just wasn't doable mechanically. Hence why scroll wheel ergonomics became a bit of a fail. Granted, the lil' Logitech isn't much worse than the MS oldie if you hold it the right way, but still, isn't that interesting?
JFTR, I don't exactly have small hands... fairly long fingers, in fact.
