P: Is there an optimal setting for Select and Mask? I can never get it to work efficiently :-(

Adobe just released PS 19.1 with changes made to the Select & Mask tools to add a Decontamination control. Perhaps the changes may improve performance. Give it  a try and let us know. BTW- No issues on my similar Windows 7 system with a low-performance Quadro 600 GPU and 2.8GHz i7-860 quad-core CPU.

And here I am thinking I have a "decent" machine. I agree with you, there is no point to use quick select on the detailed stuff on an image like this and that's the approach I would usually take, too. I just thought I'd do it all in Select and Mask and also start from selecting what I want to keep to show the extent of the issue. Before replying, I thought I'd use QS first and go through that process, starting with the Quick Select on the background, then invert but once I got into Select and Mask, the problem persisted when using the refine edge brush. I also think that Quick Select should be faster i.e. no spinning ball. To be honest, I use a much lower spec machine at times and it's all quicker on there

Thanks Stefan, I am afraid it is still as slow as this 

Cheers Todd. It was not much of a difference I'm afraid. In fact, it took about 5 mins again before I gave up. Anything else i can try? Also, yes, starting with the Quick Select on the background is quicker initially but once you get into Select and Mask, the problem persist when using the refine edge brush. 

Ouch, that looks painfully slow. Do you have any setting active in S&M though? It's always better with that tool to have everything zero'd out when making the initial selections...

It's much more responsive for me (though I have a powerful machine - but it has always been fast), even on high res images. But I often experience that you need to plan how you mask nonetheless. For an image like you show in the video, the best would be to first select the outside area which is a flat color (much easier for photoshop to calculate) then invert the selection and start to finetune after. Also using magic wand or even lasso in the beginning and then move on to quick selection tool for the minor details and then enter "select and mask" mode screen for fine tuning. Usually this way I have masked an image perfectly within a few seconds. there's really no point to use the quick selection to mask out every inside detail. 

Jerry,
that ́s terrible 😞
On my system it ́s nearly realtime. You could try a bigger radius for the QS tool. Is it as slow as this, if you use other preview modes (on black, on white etc.)?

Try changing PS Preferences> Performance> Advanced Settings as shown below and Restart PS.  Also try using the Quick Selection Tool on the even toned background then click on 'Invert' and use the Refine Edge brush at the hair line.

And that's what I just did after trying for minutes - cancelled and went back to the old 😞 

I must admit, I have the same problem as you. It's so painful that I always cancel and go back to the old method.