Those are wonderfully large SSD drives you have.
Prices have come way down... A 2TB MX500 is now $207 on Amazon and a 4TB 860 QVO is around $399. Plenty of 1TB drives under $100.
SATA III SSDs are just as fast over USB 3, 3.1, Thunderbolt 1/2/3, in a PCI card, SATA, eSATA... the SSD is the bottleneck. I get pushback whenever I post this but I've done the bench testing that proves this.
But if you feel ‘the need - for speed’, check out PCie drives. That’s my next wish!
On the boot drive, oh yea. A fast 2TB 970 EVO is down to $479 while the slower 660p is now under $200. For external or additional internals, a waste of money for music production but, if doing video, heck yea.
Here's what they don't tell Mac owners: Over Thunderbolt 3, the maximum number of data lanes is 4. A single NVMe 3 x4 blade in a Samsung X5 is about as fast as a pair RAID 0 in a twin enclosure (the slots become x2) or a quad where the slots become x1. Fine for JBOD but not for speed.
If I needed PCIe storage, I'd order up a Mac Pro in a couple of months and sell my iMac Pro. I'll assume that your PC could take them now. With fast blades such as the 970 EVO, it'll scream. Even the slow, inexpensive blades such as the Intel 660p have way more than enough giddyup for audio. I installed a 660p into my daughter's mid-2015 MacBook Pro and that rocks over the AHCI that Apple installed.
SATA III externals are fine for anything I'm doing now and, if I needed faster, a 2TB X5 is $800—with 2 TB3 busses, I could connect a pair without a speed hit.