Any idea how that works? More processing power shouldn't really help with loading times unless there's decompression to be done, I would imagine.
I would imagine the increase in clock cycle speed for the CPU and faster bandwidth for the RAM are primary contributors; these things are both "unlocked" in beast mode where as at the standard operating level, they are hard capped parallel to the OG PS4 for legacy titles. More gains would be made if you switched over to SSD, as the Pro has a SATA 3 bus over the OG's Sata 2.
Honestly though permalite would be the dude to ask.