Hi Andrew,
BootROM 1.0.5.7, which is currently installed on slot 1 of the 2-node stack is the latest BootROM for the X450e switches. Since you have a 2-node stack of the same type, to avoid any unexpected side effects in case of a stack node failure/failover you can consider upgrading slot 2 to a matching BootROM as Slot 1, and then reboot Slot 2 for the BootROM update to take effect (ideally during a short maintenance window).
Thank you.
Best regards,
Andrew