I would love to see some example comparisons made by others.
The space page Find Your Doppelgänger is open for editing by the community, but you can, of course, also post here in G2G.
Click here for the image details page or here for the full-sized version (1259 x 745).
Edit: on the space page I show comparisons of mother and daughter (the pic above, 41% likeness), two sisters (53 % likeness), and my grandfather at two different ages (95% likeness).
I actually do look quite a lot like my maternal grandmother, perhaps more if I would compare photos from a younger age. I'll see if I can find a couple with reasonably similar angle.
The Twin Strangers website seems to rely heavily on same-angle photos.