Hi Geoff
I think your larger peregrine is the migrant race calidus, which is known to be larger and paler then the resident peregrinator. Paer birds also have a tendency to look larger which probaby enhances the actual size difference.
I've never seen both races together, and I certainly envy you the sighting!
Cheers
Mike K
Mike KilburnVice Chairman, HKBWSChairman, Conservation Committee