There is apparently some sample variation regarding edge performance.....in this thread, Manolo's turned out to be out of spec and Leica addressed it to some extent... http://www.l-camera-...st-impressions/
Regarding your comparison to the SL 24-90, you omitted the image stabilization of the SL zoom, which is especially important for handheld use. Handheld, the faster SL zoom, coupled with both IS and AF, should be easier to obtain sharp results in less than ideal light... aided by its better edge performance and weather sealing. A sharp smaller file beats a fuzzy larger file.
I demo-ed the S006 and 30-90 for a week last Summer, but was disappointed with handheld results in all but good daylight. This was exacerbated by the optional spit image screen in the S006, which tended to half black out when using the longer, slower end of the zoom. For tripod work, at faster speeds, this of course would not be an issue. I'm sure that the zoom coupled with the newer, faster S007 would have fared much better for handheld use.
1. There is sample variation indeed; I mentioned that I found a good used copy, before that I tried a not-so-good one which was from a lens test pool and was decentered; but in the name of fairness I didn't mention it in the article because the lens obviously had a rough life (looked pretty knocked);
2. About the SL, I said "If you are a Leica SL owner and you don’t own or plan on owning a Leica S, I would definitely recommend getting the SL’s native 24-90mm Vario-Elmarit-SL over the 30-90mm Vario-Elmar-S. The 24-90mm Vario-Elmarit-SL has amazing image quality, it’s wider, faster, lighter, easier to filter and its AF is much faster; at half the price of the 30-90mm Vario-Elmar-S it’s a no brainer. However, if you are a Leica S owner and you either already own or are thinking about getting a Leica SL for backup or to complement your S system, the 30-90mm Vario-Elmar-S is a lens you might want to consider: not only it works perfectly on the Leica SL, but here the corner softness at longer focal lengths is all but absent.".
I never compared the 24-90 on the SL with the 30-90 on the S; I compared both lenses on the SL only, and strongly recommended getting the 24-90mm, so I don't see what your point exactly is: we seem to agree on this. However, perhaps I didn't explain myself very well, or you didn't read that part of the article with enough attention: since both lenses are used on the SL as you can see from the paragraph above, I don't see where you get your "A sharp smaller file beats a fuzzy larger file", since both files are actually from the same camera, the SL, and therefore are of the same size More, the Vario-Elmar IS weather sealed as the 24-90mm, and it has great corner-to-corner sharpness on the SL, where it uses only the central portion of the image circle.
Btw, I'll add image stabilisation in the 24-90mm advantage list, thanks for that - obviously I forgot to include it.
3. About your last sentence, I used it on the S 007 only, so I cannot comment on the lens' performance on the S 006, and even less so if you add a split screen instead of the original screen. Of course, AF in low light with a f/5.6 lens is going to be poorer than with a f/2.5 lens, and of course handholding a f/5.6 lens on medium format in low light is going to be tough - no surprise there. I also don't understand your "For tripod work, at faster speeds, this of course would not be an issue.": if you are on a tripod, you'd use SLOWER speeds, not faster speeds for which you don't need a tripod at all.