Ah, that really helps, Ivo! Didn't realize you were tricking us the whole time with some square root thing.
So, roughly speaking since 1.8 HDR is new and improved, old-HDR was starting out at a context size of around 31 or 32.
Brendan I looked at your data and log, and they don't seem to match up. ?? Rather than the Cocoon, the FITS file is the Bubble.
And when I did my Cocoon, it wasn't super amenable to HDR anyway.
But I still ran things through and found out some stuff. The underlying data makes some difference, but not a lot it seems. Resolution, however, does. Makes sense.
I'll just type out the results, since I just write stuff on yellow pads. No nice code insert or spreadsheet like you and Guy have.
Testing was on an i7-6700, which I think is 3.4/Turbo 4.0; 32GB. If it matters, which it might not, while the data is opened from an HDD, the OS and ST are run off of an nvme 1TB 970 Evo Plus SSD, and the lame GPU is a GTX 745 OEM with some Afterburner.
I matched your bubble data with the same crop/bin/wipe/A-D/contrast defaults and went into HDR at 1779 x 1109.
Low Q: 50px - 0:46 60px - 1:35
Med Q: 50px - 0:47 60px - 1:39
HighQ: 50px - 1:42 60px - 3:44
I also ran at 40px at Med Q: 0:20, and High Q: 0:44, to compare with Guy's percentages. As you can see, I was showing in the low 40% range rather than his 50%, and that held up in further testing. Obviously this is all pretty ballpark-ish.
Then I accepted one, colored it with defaults, and ran SS, which took 0:28.
In order to compare to a busier dataset than your widefield bubble, which was pretty sparse, I loaded the ST Orion data, and binned/cropped to the same 1779 x 1109. Also, the M42 is far more amenable to HDR.
Low Q: 50px - 0:50 60px - 1:42
Med Q: 50px - 0:50 60px - 1:46
HighQ: 50px - 1:53 60px - 3:55
SS took 0:27.
Reviewing your numbers and mine, the percentages run fairly close, and we can probably add estimates to those Guy already made. Assuming context 50 to be 100%, context 60 takes about 200% time, context 70 360%, and context 80 640%.
Low and Med Q both take approximately 40 to 45% the time of High Q (lowering slightly as the context rises), but are in fact so close as to not really be worth using Low Q, except for some small gains as you increase the context level to maybe 75% or higher? Possibly then there's some room to make some adjustments here, because I'm not sure it's otherwise terribly useful to have the Low Q.
I then ran ST Orion again, but at double (quadruple really?) resolution of 3558 x 2218.
Low Q: 50px - 3:06
Med Q: 50px - 3:08
HighQ: 50px - 7:01
SS took 1:53
I didn't try out the other context sizes, but I think everything is already falling into place. Low and Med Q are in this case 44% of High Q. And everything is taking very roughly 4x what it took at the lower resolution.
It all seems fairly predictable, so if you try it out and get a certain amount of time for your machine at the default setting, extrapolating an estimate of processing time for different HDR context and quality settings can be done, including varying the resolution on another session with a different binning level.
That's all I got.