Have you considered natural Goat Hair Brushes for your project?, they seem to perform magic if well constructed.

hi thisisnotatoy Not too familiar withthis brand of brushes but I f I have it correct the one you refer to is a synthetic version of mongoose hair? I have a brush like this but a different brand I also have real sable brush (all be it small:)) but I found the difference the mongoose slightly stiffer than the sable (as correctly said by others here you need to be going softer not stiffer if you want to omit brush mark)obviously sable is like a dream and would be perfect for what you are trying to achieve .I would steer you more toward a synthetic sable not a synthetic mongoose as sable(I find anway) works better for not leaving a brush mark it’s like magic no matter what you use it for never leave not one mark beautiful.Also you would be better of not maybe with a bright but with a softer less chiselled end because anything to precise and flat like a cutting in or that kind of thing can leave track marks form edge of brush..but you want precision also so go with a small genuine sable for your detail and synthetic for your larger areas this would cut down on cost.But if cost is not an issue I would go with pure sable all the way.Personaly I have not found an imitation sable brush yet that can do what a sable can so I rather tend to try to find alternative ways to change the paint to make it compatible with a synthetic brush rather than other way round in order to cut costs , iv’e seen a large sable brush but it was in my dream lol