One thing to be aware of when using the SfW or Lr is that Adobe still only have 13 actual levels of JPEG compression. So Q70 to 77 equates to level 9 and 78 to 85 are level 10. To get to 11 you need to go to 86, the highest level is 93 upwards. Remember that for both scales they go from 0, so 0 to 12 gives you 13 levels and 0 to 100 gives you 101 levels.
So although I use Q80 I could just as easy use any other value between 77 and 85 for the same identical result. I have no idea why Adobe would go over to using a 0-100 scale, with only 13 levels of compression, especially when they still use the 0-12 scale widely too.
When it comes to the actual compression effects level 10 seems to offer just about the ideal. I did some comparisons using images saved at all 13 compression levels, plus an 8 bit TIFF file. Even when you save a file at the maximum quality as a JPEG, with no compression, you still get conversion artifacts because the JPEG file does not store the data as RGB triplets, it uses luminance and chrominance values in a similar way to how analogue colour TV works.
In my tests as well as judging the image quality by eye I did numerical evaluations by putting all of the images as layers in a Ps image. By using the difference blend mode you can actually measure the difference between any two versions of the image. When comparing both the Level 10 image, and the level 12 to the original TIFF file version the size and distribution of the differences is pretty much identical, with a large majority having 0 difference. The differences that do exist are generally within the range ±2 with maxima being about ±6. Oddly if you compare the level 10 with the level 12 they have a higher range of differences than when you compare them with the TIFF.
The great advantage with using level 10 is that you get somewhere between a 60% and 40% reduction in file size on disk, compared to the uncompressed image, with minimal measurable degradation, and absolutely no visible degradation at least as far as I can see. As I have said before I now never use higher than level 10 when saving files as JPEG, even when sending the files out to the lab for printing.