I know it's unlikely given how size and cost conscious console vendors are, but a 2TB 7200 3.5 inch (single platter) mechanical HDD would give about twice the throughput of the 1TB drives in Pro/X and have lower access times to boot (shorter seeks, lower rotational latency).
For any given HDD technology, the 3.5 7200 drive will always have a big increase in throughput and lower access times (so long as data is arranged remotely sensibly on the HDD).
So for an extra $10 you double HDD throughput, and negate the need for an SSD, but you would require a slightly larger case. And most USB drives wouldn't be fast enough then to act as external storage.
For any given HDD technology, the 3.5 7200 drive will always have a big increase in throughput and lower access times (so long as data is arranged remotely sensibly on the HDD).
So for an extra $10 you double HDD throughput, and negate the need for an SSD, but you would require a slightly larger case. And most USB drives wouldn't be fast enough then to act as external storage.