I believe it is most charitable to hope that all will be saved and to assume that none will be.
With the fathers of the Church and a great number of older saints, it’s basically a non-issue: it is believed the great majority of souls are in Hell. However, I do believe this should have limited import, because if you raise up a number of students in the same class, under the same teacher, in the same culture, the result is going to be that they’re pretty much all going to think the same way and hold very similar opinions. A 4th century Catholic theologian isn’t going to go around talking about how few will be damned when everybody he ever knew held a contrary opinion; it is extremely doubtful such a view would ever form within him, especially if we consider that Christians assumed the pagan nations (which was the enormous majority of the world compared to the Mediterranean) were damned by default. So stacking up a large number of quotes by older saints isn’t, in my opinion, very meaningful or compelling. They were all cut from the same stone.
Still, even if we set that aside, the strongest case for the majority being damned always has been, and I think always will be, the words of Christ himself. Saints are weak, but the Gospel is not, and is created for all time, and Christ says that the gate to Heaven is narrow, and the road to Hell is broad. Many theologians today, who certainly cannot by any stretch of the mind be called lukewarm Christians (Pope Benedict XVI among them) conflict with the old, literalistic interpretation, and speculate that Jesus is speaking as an anguished father towards his children, rather than as a statistician. But without any infallible declaration, this explanation will remain speculation. I suppose I could see that as feasible.
It is best to just focus on loving God with all your heart, body, mind and soul, and being a light to the world, and allow the Judge to handle the wet work.