[Performance in PHOTO super slow on MAC]

No, the warnings are for hard-drive usage, which isn't usually a problem.

Did decreasing the RAM size help at all? I cant see one image using all of 16gb no matter how many layers you have, but Affinity might try and grab the whole 16gb for itself which would certainly cause problems. 

Lowering the RAM value is worth a try at least.

[Performance in PHOTO super slow on MAC]

Do you actually have 16gb of ram on your system?

Try to set the RAM amount to about 70% of your physical RAM size in your machine.

[before/after]

Does having a 'before & after' viewing tool count as bells & whistles or as an essential tool of editing a photo?

For me, comparing my edited version with the original is just something I do time after time after time, if not with Lightroom's built in tool then with windows photo viewer (that i have to do when using Affinity). Sometimes an edited copy isn't all that better than the original so I'd dump the edit, or find something more creative to do with it.

I think comparing before and after is fairly essential to the editing process, but how essential is it to have as a TOOL?

Any thoughts?