More Than Twenty Percent

The story is told of a man who approached a rabbi. He said to him, “Why are you always so machmir? Every time I ask you a question, the answer is always that it is forbidden.”
The rabbi said, “I’m surprised to hear you say that. I indeed have many kulos! For instance, many rabbis say that one may not fast on Shabbos or Rosh Hashana. I hold that one may. Many rabbis rule that one should not learn Daf Yomi on Erev Tisha B’Av in the afternoon. I hold that one may. Many rabbis are of the opinion that one is not allowed to sleep in the sukkah on the night of Shmini Atzeres. I say that it is permitted and encouraged. Some rabbis are of the opinion that one should not cry on Rosh Hashana. I hold that it is permitted. Finally, some rabbis are of the opinion that one should not give more than twenty percent of his money to charity. I hold that it is permitted. Of course, I need to be machmir in other areas to counterbalance these numerous kulos!”
The Gemara in Kesuvos (50a) records that when the Sanhedrin was exiled to Usha, they made numerous enactments. One such enactment is that one should not give away more than twenty percent of his money even for charity. Yet, the Gemara in close proximity records two instances where this rule was seemingly ignored.