I think there's a potential problem with how voters perceive the nature of the poll. For instance, does everyone start at 3 and have their performance rated against their own ability or is there some notional yardstick where 3 is an average for a premiership player in that position, so Robshaw may start as a 4 whereas Lambert may start as a 2 and then get rated up or down from there.
DOK, perhaps you should get voters to rate a player's ability from, say, 1 to 3, then rate their performance out 5. You could then calculate their adjusted performance rating from the natural logarithm of the square of the performance divided by the natural logarithm of the square of their ability. This may give a more accurate reflection of whether someone played like a donkey. Or not