So, at the end of the day, I whimped out. I had every intention of buying and SP4 and making it my main system, but I wound up buying something very different - an almost maxed out Macbook Pro 15. Still, I have a strong feeling that I'll be switching in a year or two, if Apple keeps up with the schizophrenic view of computing.
This step was about me switching from a desktop to something more mobile. Though my work issues me an MBA, that's not been powerful enough. So I do 70% of my computing on an i7 iMac, only using the work system for those tasks where security/vpn are huge issue, and I need a corporate-owned resource - less than 5% of my work. My personally owned SP3 takes on the rest of the load, where I need a Windows system or when I'm lounging about in the house (I much prefer it to my MBA). But, at the end of the day, it would currently be too diosruptive to switch the platform that pays my mortgage, and the family is kind of locked into the ecosystem.
Issue is that I have two catalysts forcing me to make a decision in the next few months: woman's MBA broke, and Applecare on my iMac is almost expired (I sell them under applecare, when I refresh).
So, I'm swapping the iMac for a Macbook Pro. I got the MacBook Pro as a refurb, which cost me ~$2,250 (2015 i7/16GB/512/AMD GPU). I suspect that my 2015 iMac will fund half of that, as it usually does in my refreshed (great thing about macs). And I'll now bring my main "desktop" with me while traveling, or just wrestling with the kids.
But honestly, if Apple keeps up with the multi-OS view of the world, my next workhorse will be Widows. And I don't plan on waiting another 2.5yrs for my next refresh. And I'll be spending a lot of time with my SP3 in the coming months, as well as investigating alternatives for the Apple ecosystem. I'm still a fan of Microsoft's vision, vs Apple's.