The big question here is why you want the larger harp space. If it is to facilitate the actual quilting (rather than piecing) process, I would suggest you not replace your present, beloved Bernina, but use her only to piece. And then look at what would be your best choice for a dedicated quilting machine....which only needs a straight stitch.
When I went through this process (my main machine is a Bernina 170 I bought used off EBay...love that machine!) I kept my old Bernina 170 as my piecing station and got a Juki 2010Q as my quilting station machine. Eventually I decided to take the leap and bought a used longarm (a Grace Q'Nique 21 setup), but I still use the Juki for smaller projects.
When I was pondering replacing the Bernina with a new model with bigger harp space, my machine tech strongly advised I stay away from the larger Berninas. They were not performing well when first introduced and he correctly pointed out the extra harp space was not a big improvement over what I already had. And the big Bernina's are crazy costly. The Juki was really affordable, a great machine.
You could also consider a sit down machine like the Q'Nique 15, an attractive option if your free motion skills are good and you don't want to swap over to the longarm and its different skill set. I think Leah Day has some YouTube videos on her experience with that kind of setup?