Thanks guys! -
XO 'crept up' on me unexpectedly. It had faded a bit out of my active consciousness and is returning there. The comparison with Pet Sounds above isn't far-fetched... I once bought PS on the recommendation of my then favourite music mag. After a few spins I thought: 'OK, the opening tracks of side 1 and 2 are pretty good... and I thought nowt much else. Boy, was I wrong about those 11 other songs... PS is my all time favourite, and in second place are 'BWPS', and/or a purely mental exercise with all that's left from the original SMiLE sessions.
'Song Cycle' is #3, 'Discover America' # 4.
For the sake of precision and properly reasoned qualification/quantification, I see no records at spots 5 to 20 in my list. And at #21 the ranking continuous with some King Tubby and Television.

...great talent, left the planet early. I only have 'XO' and rediscovered that just these days. And: 'Figure Eight' is available in the sales now for a bargain basement micro-stash of cash. Should I invest?