I wish I could help out here. I have a Skylark that I have written about many times here, and a Further on order - so I won't really be able to make any kind of specific comparisons until I can play the Further through my equipment at home. The electronics are different, and I'm sure the Further offers even more flexibility of tone than the Skylark, but I cannot comment fairly on what the difference is like. The Further also has an onboard effects loop, which the Skylark does not.
In terms of scale - my Skylark is 25.5 and the Further will be as well. From my limited experience with a Further the feel of the neck was pretty much identical to my Skylark (keep in mind, I didn't have my Skylark with me when I played the Further - so, no real A B comparison was possible).
Furthermore, I'm sure it is not uncommon for any given Alembic to sound somewhat different from any other (even the same model), given that they are not stamped out on a conveyer belt. If you check in the factory to customer section right now, you will see a handful of Furthers with different features and wood selections, not the least of which are neck laminate choices which diverge from the standard combination on the Product Page.
Many have suggested that a Further will have greater sustain due to the through-neck design, though I feel my Skylark has excellent sustain. The Skylark is clean and bright sounding (I can even get a very convincing acoustic guitar sound out of it), and I'm hoping I will get a wider variety of dark, warm tone from the Further. I'm also looking forward to having the effects loop control at my fingertips.
Both of the Alembics I've ordered are at least a little different from the standard model in the product section of the Alembic site, and this is really one of my favorite things about Alembic. I consulted with Susan and Mica at great length prior to ordering either guitar. Susan advised on wood and features to achieve what I was after, both musically and aesthetically. I suggest you give them a call and let them know what you're looking for and what your budget is and let the experts guide you through your order. You will not be disappointed.
Tom