If you are halfway through researching your current tech and you have two RAs finish on the same turn, that is 100% of the median amount of the available techs. That means the median tech and any below that would get finished in one turn with no research into it at all. So depending on how far into your current tech you are and if you have already put research into another tech, you could potentially get two techs on the same turn from the RAs.
The only way you wouldn't have any overflow is if you had just started researching one of the more expensive techs available to you.
This also doesn't take into account the Porcelain Tower or Rationalism.