Do not assume that an apple with high brix is sweet. A lemon has plenty of sugar and if an apple is high acid it can be tart with lots of sugar also. Goldrush has about the same brix as Fuji which I think is what makes it such an appealing apple to me- that and the denseness of its flesh. I believe that some of the great tart English apples like Cox are also very high on the brix.
Anecdotally I assume that brix and flesh density are the determining factors in what holds the flesh together after hard freeze. I have never seen a study on the subject, however.
[NAFEX] Brix and frost protection,
Alan Haigh, 11/05/2008