Deer Park: a rather large Peregrine

I looked out of the kitchen window a couple of days ago and spotted a very large brown/grey bird sitting on a fence post on the Coast Path above Renny's Slip. "Buzzard", I thought, but picked up the binoculars whilst waiting for the kettle to boil. In fact it was a Peregrine, which promptly flew and sat on the Deer Park wall. Three things fascinated me about this bird:

1. It was massive. I have seen smaller Buzzards on exactly this spot. To scale the photo, the post to the left of our gate (where the latch is) is 44" tall above the grass. Where the bird is sitting is 10-12 feet behind the gate
2. The huge amount of black on the head. This is not so much a "moustache", more a complete "executioner's hood"
3. The large, almost white, triangular patch on the top of the breast, before a fairly clean demarcation to the more classic spotted Peregrine breast.

I am (just about) prepared to accept that this is a female Peregrine at the limits of normal size and plumage variation: it is a stunning bird, so keep your eyes peeled (the sky may darken as it flies overhead!). However, I wonder if there are traces of some more exotic large falcon in its ancestry? No sign of jesses, though.