i personaly defetly think not
but once u are crit capped like 79.8% u competely loose the crit part fo agility
i saw in someone's BiS list he nechant haste rating on his cape instead of agi and it was verry surprised
(http://elitistjerks.com/f73/t63774-cat_dps_guide/p27/)
but if agi gets so bad will mongooze still be best enchant ? i gues it will be bezerger then