Taken from Gleason L. Archer, A Survey of Old Testament Introduction (Chicago: Moody Press, 1994 ed), p. 32.
"Even though the two copies of Isaiah discovered in Qumran Cave 1 near the Dead Sea in 1947 were a thousand years earlier than the oldest dated manuscript previously known (A.D. 980), they proved to be word for word identical with our standard Hebrew Bible in more than 95 percent of the text, but in 1QIsb, (ca. 75 B.C.) the preserved text is almost letter for letter identical with the Leningrad Manuscript. The five percent of variation consisted chiefly of obvious slips of the pen and variations in spelling. Even those Dead Sea fragments of Deuteronomy and Samuel which point to a different manuscript family from that which underlies our received Hebrew text do not indicate any differences in doctrine or teaching. They do not affect the message of revelation in the slightest."
You can find much more evidence in this work.