You are thinking of each of these octave runs as part of an entire chord, right? So, not just "plunk" one, "slam" two, etc.?
Thanks very much for your reply, and I'm glad you know the piece so well! I totally get what you're saying about not thinking in terms of 'hands separately' in the main theme sections. I think it's especially true in the hand crossings. I think the latter is more accurate I find it hard to transate thinking of the octaves in terms of chords into playing them still in a relaxed way, if that makes sense. Anyway, I'll try to approach it mentally like that next time I practise!