I recently read an ESV reviewer who said the amount of difference between the RSV and the ESV was about 4% or so, if I remember correctly.
However, on occasion those "4%" seem to rather significantly improve the passage, imo. Here is Hebrews 1:1-4, first in the RSV then in the ESV. See if you like the differences.
In many and various ways God spoke of old to our fathers by the prophets; but in these last days he has spoken to us by a Son, whom he appointed the heir of all things, through whom also he created the world. He reflects the glory of God and bears the very stamp of his nature, upholding the universe by his word of power. When he had made purification for sins, he sat down at the right hand of the Majesty on high, having become as much superior to angels as the name he has obtained is more excellent than theirs. (RSV)
Long ago, at many times and in many ways, God spoke to our fathers by the prophets, but in these last days he has spoken to us by his Son, whom he appointed the heir of all things, through whom also he created the world. He is the radiance of the glory of God and the exact imprint of his nature, and he upholds the universe by the word of his power. After making purification for sins, he sat down at the right hand of the Majesty on high, having become as much superior to angels as the name he has inherited is more excellent than theirs. (ESV)