In all honesty, and not just because I have one (single CPU not dual though), I still find the 4,1/5,1 dual CPU models to be a better bang for the buck than the TCMP. They lag not *too* far behind when fitting with high end 6 core processors, can still have a proper NVMe drive, and way more graphics card & expansion card options. Hell you can even add TB3 to them (kinda clunky with the rebooting thing but still an option, and quick with an SSD).
I've only got a single CPU model with an X5675, but filled with an RX570, USB 3.0 card, USB C card, 1TB NVMe SSD, 2x 1TB + 1x 1.5TB + 1x 240GB SSD, and 32GB RAM. It's an 11 year old computer at this point, but with the modern expansion & graphics card you genuinely wouldn't know. All in, I'm in this one ~$500. Tack on another $200-$300 for a dual CPU model (cost of the unit + extra CPU + extra RAM that you will of course want!)