20 to 25 lb of food (11 kg to us Europeans :-) ) is a wee bit excessive to my mind. Thats why I am saying 7 days and it will probably be closer to 10 lb if I can get some sandwichs, snacks and crisps on the way (so now I am sure everything will be OK) - the more I carry the less chance I have of doing it but each day I walk the load gets lighter anyhow. I always tend to pack heavy anyhow (35 lb) which is maybe why I only average 10 mpd. The water I can live with but the heat could be difficult espically if its high humidity as well.
Maybe I will try the PO forwarding as a back up as it wouldnt hurt sending a few lb of food - but I am always a bit nervous about relying on this though.

"Hey ho, onwards and upwards apart from the downhill parts" was what my old headmaster used to say - mind you he died on Mont Blanc when he fell of.