Joining a top tier consultancy will not help you become a great PM. Full-stop. Yammer has one of the best product management groups and although some of their PM's have left (since the Microsoft acquisition), they still have a great group there. Some of Yammer's best PM's started out in different non-product roles.

There might be some junior roles there that get you on the right track. There are a number of great established product teams that are always eager to add team members who are hard-working, passionate and eager to learn.

Happy to talk to you in a call to point you in some specific directions but joining a great product team that actually *owns* the product is way more instructive and a better career path than a top tier consultancy.