There are clearly extenuating circumstances, but I think the academic evidence would need to be compelling - more than predicted 5s and the headteacher's support.
See http://www.elevenplusexams.co.uk/11plus ... rs.php#b11
Evidence of reasoning ability at around 90th percentile might be useful, as would the strength of the headteacher's support (and the way in which he chooses to word it).
Level 5 covers a wide range of ability, so 'sound level 5' predictions would be better than 'level 5'.
Come back if you'd like to discuss further.