In Best of Both Worlds, one cube wiped out the Federation fleet, and, if the Admiral was to be believed, some Klingon ships as well. So a massive fleet of many cubes would have destroyed the Federation and, probably the Klingon Empire. But could that also have destroyed these two and the Romulan Empire? I'd say yes, because that makes sense.
Then there could be the issue of these three plus the Breen plus the Cardassians. I'd still say the Borg could win, because one cube can take out the Federation (almost), then hundreds of them can take out the entire quadrant.