Bleach's power level is pretty fucked up right now. Ichigo is peaking or seem to be peaking faster than everybody else. How will The Shinigamis(SS) beat the top 5 espadas?? I don't think Kubo will change them into hybrids.
i think that Ulquiorra is probably between or equal to rank 4 to 1. Right now the mission he was assigned to the highest number was 5 and Ulquiorra was the leader so it's safe to assume that he is higher than 5.
No matter what Hitsugaya does, he is still in the dog house. Just when we thought he managed to defeat a high ranking ennemy, we find out that the guy wasn't dead, only frozen.
Also as urahara mentionned, i think it will be a Battle Royale, where every single captain, karakura high(chad, ishida), vaizard, Non SS shinigamis(urahara and Isshin) will get an opponent. As to how the'll beat Aizen? i got one answer for that: shounen. when things will go bad to worse and things will seem to be coming to end, Ichigo will get a last minute powerup and beat Aizen.