1) There is not really a path to partner: either you make it or you don't. Some partners are horrible managers and some wondeful managers will never make partner.
2) Boutique definitely gives you more responsibility faster, which can lead to a quicker partnership.
3) But beware, since at some firms "partner" is just a title with no equity stake associated.
4) The people that really are meant to be management consultants (about 2-3% of management consultants) will make partner fast at any firm. A small minority of the other come under 2). The rest will not make partner. Most of the latter will learn not to want to make partner.