I decided to test the load times between different models of the PS2. Both consoles are NTSC-J region and I tested them both with the Japanese version of the game.

Although I haven't tested it I am pretty sure the load times for PS1 consoles will be the same as the phat PS2 models.

In conclusion the 90K PS2 with PS driver 2.00 is the fastest for loading.

Left is SCPH-90006 Right is SCPH-50006.

This is the BIOS for each console.