The privileged people in Saigon fleeing the new regime escaped mostly via connection. For example, I know people here who fled on US airplanes/ships. They were educated, and most likely knew some French/English before coming here.

The "boat people" were more likely from the coastal town (like Vung Tau), who dropped everything and got on tiny boats, packed like sardines, hoped to get rescued from other fishing boats when getting out far enough to the ocean. They are often poor folks with nothing to lose, and willing to accept a coin flip chance between death and escaping to the US. For this part, I don't have the concrete statistics. But from the stories I have heard, the survival rate of those boat escapes is worse than 50%.