Using the lenses as loupes, they look great. Super flat-field of view, absolutely no pincushion or barrel distortion apparent (uncannily flat in fact; never seen anything like it). A very wide imaging circle apparent from looking "round the edges". At first I thought I got a couple of duds though. Despite being able to clearly focus the image at a distance of around 60-80mm (with the eye at any distance behind the lens when used as loupes) I needed at least 200mm of extension tubes to be able to get a focused image on the sensor at a working distance measured in something less than feet. I used the extension pictured below (right hand panel) and added a further 100mm to get a mag difference for the FL and F-Stop calculations.

So it seems these are "infinity" lenses. At least, putting them on a tube lens brought the working distances down to a reasonable 80mm and 60mm respectively, so I assume that makes them infinity. I only have adapters for my 135mm tube lenses, and this gives mushy corners. I'm pretty sure the sweet spot will be a 200mm tube lens - but for the upcoming tests, I'll use 135mm tube and APS-C crop mode as that will be close to the FoV of 200mm and FF. Here's the 92/7.1 lens mounted on the rig. Both lenses slotted neatly inside a bit of T2 extension tube with PTFE to snug them in place.

And here's the first (full frame) stack taken with the 115/5.2 lens. I used 140 micron spacing, about 80 images, PMax with no retouching.

First impressions: the 115/5.2 (1.08x on 135mm tube) looks sharper than the 92/7.1 (1,44x on 135mm) and vignettes a little less. Some of the vignetting comes from the tube lens but I'm not sure how much is from the scanner lens being pushed down too low. To be investigated. The longer focal lengths are great for stacking as there's less perspective scaling so far less image is lost to edge-streakies. The lenses don't "see round OOF edges" as much either, so far fewer issues with overlapping features looking semi-transparent after stacking. That should be a bonus with hairy insects.
I have a couple of Raynox lenses somewhere. Isn't the DCR-150 around 200mm? I wasn't too pleased with their image quality when used with Mitties, but perhaps it will be better here. I need extra adapters for that though, and have to read up on spacing of the Raynox from the sensor, etc, but 200mm would take the lenses magnifications to 1.6x and 2.1x respectively. Bang in the range I'm looking for. Sweet
So off to testing next. In the intereim, I'd be interested to hear any comments on the specs so far. Assuming image quality checks out, would these be considered good? They look it to me.