Dave,
I, personally, would not use the 25000 spools. On a few occasions I have seen them bend the spool shaft, jamming the spool against the rotor (which is what happened with Jussi) when hooked up to a fish whilst using heavy drag. You do not need more capacity than what the standard spools carry when fishing for GTs and I think the standard 18000 and 20000 spools do the best job.
Somebody who is an expert on JB Hollow (not me) can tell whether the line is suitable or not. It may actually have a breaking strain above 80lb, I've no experience with it so don't know. However, I would not fish Southern Oman with less than PE8 (usually 100lb+) and ideally PE10 (120lb+).
Hope that helps.
Regards,
Trevor