The so-called Long-term Economic Impact study – which like all such studies necessarily employs a range of simplifying assumptions – suggest that a 1% lowering of the yearly probability of a major financial crisis corresponds to an annual output gain of 0.6%.
Of course, these figures need to taken with a pinch of salt, but they suggest that the order of magnitude is very significant. The same study suggests that, depending on the level of capital requirement, an increase of 1% in that capital requirement has a significant impact on this probability.