3 stops is A LOT. How much are you a bracketer? If you go making similar photos at 2 and 3 stop increments, I might go for a 1 stop push and cross fingers.
Either way you are in for some "happy accidents" but mostly inferior results. Sorry to be harsh, but 3 stops in error is a lot. I for instance know the 1000th of a second at f4 is a common daylight or late day calculation I use with 100 speed chrome.... so my experience would have made me realize a meter reading of say 1/1000 at f8 to be suspect!!!