Hi Ashton... I have two five-strings, a 1978 Series I with a 32" scale, small body, fan headstock, and no omega cut (as seen in my avatar) and a 34" scale Balance K Series II with a crown headstock and Omega cut that was made six years ago. There are a number of ergonomic issues with the small body bass. It is definitely neck-heavy and the body also has a forward lean. To combat both I have to kind of lock the body of the bass to my body using my forearm when playing it. I have owned this bass since around 1984 and didn't play it for years because of the narrow neck, ergonomics and the fact that I prefer long scale basses due to having large hands. The Balance K Series bass balances perfectly and is much more enjoyable to play. I wanted a second Alembic for a long time but never felt comfortable with the old body styles. To me the Balance K body maintains a lot of the lines and vibe of the "standard" body shape of the 70s while bringing it into the present design wise and ergonomically.
You need to be comfortable with the looks of the bass you are buying, it is an expensive investment, but you also need to feel comfortable playing it. One thing though, I am not sure I have seen many Alembic players who wear their bass up high and since I do not it is hard to tell if the Balance K shape would be comfortable worn up high. Maybe someone else will chime in. You don't mention where you live in the USA but there may be a member nearby who would let you try their Balance K bass before you order. You are right about the five-string necks being heavier than the fours, Mica has mentioned that the majority of the weight of any Alembic bass is in the neck, something to think about when choosing a body shape and scale length. Good luck with your decision... looking forward to seeing what you end up with.