I believe the only difference is the power supplies. The lower-capacity model did not support N+N redunadncy for power as 3 power-supplies were required to power the unit, with a fourth to provide power-supply redundancy. With the high-capacity power supplies, the unit was fully N+N redundant with two power supplies connected to each power feed. From the hardware guide:
• Standard-capacity power supplies provide 1700 W of power each. Three
standard-capacity power supplies are required, and you can install a fourth for
redundancy.
• High-capacity power supplies provide 4100 W of power each. Two high-capacity power
supplies are required, and you can install four for redundancy.
I do not believe there are any other components (RE, SPC, IOC, etc.) which have been changed.
Ron