I have been using a pair of Big Baby 2's for almost a year now and can comment on how they perform compared to what I used before.
I used to gig with a GK Neo 212, then a GK Neo 410 and would add a GK Neo 215 for larger venues when I thought I needed the extra output, these were both driven by a GK MB800. They used to get the job done (I used them for 2 years and twice a week at least), the 215 wasn't as good for deep bass as the 410 or 212 but it did give a good low to mid range sound. I had before that gigged with a Trace Elliot 15 combo and extra 15 cab - heavy as hell.
I bought a pair of Baby's to allow me to have one for smaller gigs and the pair for larger venues, but to be honest a single Baby would almost cover all of my needs. They are amazing for the size, after around 50 or 60 gigs I am still amazed by the amount of bass they produce, and so is our guitarist. I have used them at weddings, in pubs and clubs, a week in a pit band and at a few jazz/swing big band gigs and they just deliver every time.
You are effectively looking at what I use when I have both cabs together, I had quite a lengthy chat on email with Alex and my original thought of buying a Big Twin was then changed to buy the Baby's - this might be they way to go for you as well. One of the advantages of these cabs is their size and weight, the Big Twin is still smaller and lighter than the GK kit I used to lug around, but a pair of Baby's are easier to move around and store.