Just my 2 cents:
From what I've been gathering, Luke, this is the situation: you are used to a very high spec setup capable of really large amounts of multitasking and don't want to give up your current way of doing things, so you are looking for a new laptop capable of this. There's nothing wrong with that if you can find it. But maybe it would be worthwhile to adjust your workflow so that it doesn't need an ultra-HD screen and 16GB+ of RAM? There must be some way you can achieve that.
These are the thoughts I have, in particular:
* From what I understand, you use a DE that basically tiles all of the programs you have open into whatever screen space you have, right? Have you ever tried GNOME? That might be a good replacement for that if you can get used to it.
* Is it really necessary to have all of those programs open at the same time?
* Is it really necessary to use Chrome or Firefox? There are more lightweight browsers out there, including text-based ones like elinks. Disabling JavaScript can also help a lot with performance in general.
* What if you had one laptop for openscad and other heavy or important stuff, and another, cheaper laptop for Web browsing and other stuff like that?
* I'm wondering about that SSD. Are hard drive speeds really so bad that you need one? Big SSDs are much more expensive than big hard drives. My experience with a hard drive is that it's mostly start-up times that are affected, so what I tend to do is log in and then go do something else while everything loads, and then use the suspend to RAM feature if I need to conserve battery for a short period of time.
I'd also like to point out that learning to live with less than you're used to would be really good for your public image, since after all, the hardware you'll be selling for quite some time is nowhere near those capabilities. ;) As it is now, for example, if someone says that what you're selling isn't good enough, they have you as an example to back that claim up. But if you manage to reduce your needs and eventually meet what EOMA hardware can achieve, then you would have your own example to refute that, and you would even have experience that you could use to advise people on what sorts of changes to make to the way they do things. Food for thought.