About that downgrade - I tried it. WinFlash reported I had 304 (not 307!) installed. I sure thought I'd installed something called 307 but I must have been mistaken. In any event, WinFlash to (re?) install 304 because my current BIOS version was "newer."
Might want to re-think that one, ASUS!
I've actually tried an after-market charger because I thought maybe the stock charger was the problem. Oddly, I seem to get the same or better mileage with a store-bought 1 amp output universal USB charger as I do with the stock 2 amp charger.
Meanwhile, I've update the chipset and Broadcom wifi drivers. We'll see whether that has any effect.