Thanks again everyone - really very much appreciated!

Sounds like realistically I'm going to have to give Sao Paulo a miss this time (a shame, but just another reason to go back and spend more time in Brazil in the not too distant future!).

IAN - I was thinking of maybe taking a quick look at Guarulhos or somewhere else on the way for a few hours - I'll do some research and see what looks interesting, but am definitely open to any suggestions (or indeed warnings of things/areas to definitely avoid). Another possible option is staying in Santos for a bit (I've never heard anyone be particularly enthusiastic about the place though), or going to somewhere up/down the coast for lunch and then setting off.

LTN - very good point, and actually one I had completely overlooked! (I usually try to minimize my time in airports, even if I've got access to a nice lounge, so I hadn't really considered it). A not great lounge is one thing, but just hanging about for hours before I can even go through would be pretty far from how I imagined my first First Class flight would start!

Embuexpat - many thanks for the local knowledge, I was thinking I'd probably just grab a taxi for the sake of ease. I've had a quick look and Embu looks like it could be a great place to stop off get some lunch and have a look round for a couple of hours! - will PM you shortly.