I was in your very own shoes some months ago, still am, awaiting for another MPC also.
My story goes like this, i thought that the Yamaha 4C MPC that came with the sax, needed upgrade, i acknowledged the advices like "develop your embouchure first" and said yea right, ok, i will, and then i rushed and bought another MPC, a Rico Royal A55, then a Bari Esprit II, and a Selmer S80 C**.
Guess what....after some months because of work and family and relocating that i couldn't touch the sax at all, when i took back in my hands, i couldn't blow in any one of these MPCs....except in the original one 4C...i was dazzled.
Bottomline....
1) Do upgrade, and test, but choose MPCs, in a stepwise fashion, some inches wider than the starter one, which is around 65-67 i think inches tip opening(
http://sax.co.uk/altotipopening.html )
2) Check that your upgrade MPC, has a Chamber size, somewhat bigger than the starter one you have, not a way bigger one, because you will also get dissapointed, as i have.
This way, maybe wrong way, idk, i have decided to upgrade MPCs, so when i put them in a case one next to the other, i know, which one has the smallest tip opening, or the smallest chamber size, and test accordingly which suits me best. If you get let's say 3-4 different brands with the same tip opening, before you know you really can blow through it, you would only fall into the same situation i was in, a chaotic, disorganized |MPCs buying frenzy without direction.
So buy but buy step by step

There also so many parameters for a MPC, most members here are way more knowledgeable to explain, i as an absolute beginner chose these two, for starters, keep my story not as a guide, but as an example to avoid, getting into a forest without tracks to get out.