The 1964 Alaskan quake was much, much larger and per recent scholarship, none of the New Madrid quakes were likely larger than the 1906 San Franscico Earthquake, the 1857 San Andreas quake, or the Owens Valley earthquake.
http://en.wikipedia.org/wiki/New_Madrid_Earthquake
The New Madrid Earthquake, the largest earthquake ever recorded in the contiguous United States, occurred on February 7, 1812. (The largest earthquake in the continental United States was the Alaskan Good Friday Earthquake on March 27, 1964.) It derived its name from its primary location in the New Madrid Seismic Zone near New Madrid, Missouri. This earthquake was preceded by three other major quakes: two on December 16, 1811, and one on January 23, 1812. These earthquakes destroyed approximately half the town of New Madrid. There were also numerous aftershocks in the area for the rest of that winter. There are estimates that the earthquakes were felt strongly over 50,000 square miles, and moderately across nearly one million square miles. The historic San Francisco earthquake of 1906, by comparison, was felt moderately over 60,000 square miles.
Based on the effects of these earthquakes, it can be estimated that they had a magnitude of 8.0 on the not-yet-invented Richter scale. As a result of the quakes, large areas sank into the earth, new lakes were formed (notably Reelfoot Lake, Tennessee), and the Mississippi River changed its course, creating Kentucky Bend. Sandblows were common throughout the area, and their effects can still be seen from the air in cultivated fields. Church bells rang in Boston, Massachusetts. Since the area was less developed at the time, damage was minor compared to what would happen today.
A request dated January 13, 1814 by William Clark, the territorial governor, asked for federal relief for the "inhabitants of New Madrid County". This was possibly the first example of a request for disaster relief, which would later become the job of the Federal Emergency Management Agency (FEMA).
In 1993, the seminal alt-country group Uncle Tupelo released Anodyne, their last album, which contained a song called New Madrid written by Jeff Tweedy. The song makes several references to the New Madrid earthquake.
"none of the New Madrid quakes were likely larger than the 1906 San Franscico Earthquake, the 1857 San Andreas quake, or the Owens Valley earthquake."
But did any of those make the Mississippi run backwards and ring churchbells in cities as far away as Boston?
That was something I picked up from a one hour documentary about the New Madrid fault. I'm not prepared to defend it.