I once mistakenly shot a roll of Fuji Neopan SS (100 speed) at 1600 thinking it was a roll of Fuji Neopan 1600 at a wedding. It was pretty much a 'Hail-Mary' attempt, but I did the Anchell-Troop recommended and the negs turned out very well, a bit grainy but I was amazed that not only did it work at all but I actually liked the look. For the effort I wouldn't recommend it, but it sure saved my butt that time.