[singron]

1 mostly applies to update heavy tables since index only scans use the visibility map, which would be frequently invalidated.

3 is definitely true, especially the larger the table. I've had success splitting frequently updated columns out into their own much smaller table, or any other trick to concentrate updates into a small table. Also MVCC bookkeeping requires updating pages, so an UPDATE that doesn't change any field and SELECT FOR UPDATE will cause the same problem.