One commenter makes the point that on some tests of intelligence measures, Episcopalians outscore Jews.

The evidence is mixed.

Inductivist looked at the average scores on the ten word vocabulary test included in the General Social Survey and found:

Mean IQ for whites

Episcopalian 109.9
Lutheran 107.4
Mormon 105.7
Presbyterian 102.3
United Methodists 101.8
Southern Baptists 98.0
Assembly of God 94.5
Pentecostal 92.2

In the post-Civil War period, it was common for ambitious young men flocking to New York to make it big in business to convert to Episcopalianism. That way older business leaders who were Episcopalians could see you were in church every Sunday. A lot of the converts were coming from post-Puritan religions such as Congregationalism, or from Methodism. So, Episcopalianism became very upper class. That's why some upper crust boarding schools have Catholic-sounding names like "St. Paul's" — Episcopalianism is Anglicanism (i.e., Church of England) which, due to Henry VIII, was Catholicism minus the pope and plus divorce. Arthur Hu has the 1990 average SAT scores by religion and by race. Note that scores averaged about 100 points lower than today before "recentering" in mid-1995. The two letter prefixes refer to race (Wh = white, AS = Asian, Al = All, etc.). In this, white Episcopals barely outscored black Unitarians, and were 60 points behind Jews.

Race Religion             Number   Math + Verbal SAT
Wh Unitarian              1,745    1073
Wh Quaker                   894    1037
Wh Judaism               25,600    1030 * Jewish Avg
Al Quaker                 1,009    1029
As Hindu                   4138    1029
Al Judaism               27,374    1026
As Presbyterian            3195    1022
As Angelican                197    1019
Al Hindu                  4,741    1012
Wh Hindu                     82    1004
As No Pref                17987    1001
As U Methodist              662     998
Wh Mennonite                952     990
As Unitarian                 49     986
As Episcopal                444     983
Wh Chistian Sci             830     979
Wh No Pref               99,076     979
Al Mennonite              1,063     974
As Methodist               1108     973
As Quaker                    25     973
Wh Mormon                 6,400     972
Wh Episcopal             19,555     970
As S Baptist Conv           332     966
Af Unitarian                 64     966 *Top Black
Al No Pref              137,305     963
Wh Luth Missouri          8,038     963
Wh Un Church of Christ    7,066     962
As Wesleyan                  32     960
Al Luth Missouri          8,624     959
Al Episcopal             22,109     957* Episcopal
Wh Presbyterian          32,019     956
Wh Angelican              1,765     956
Al Chistian Sci             989     955
Al Presbyterian          37,353     955* Presbyterian
Al Un Church of Christ     7826     951
Wh U Methodist           23,470     949
Al Mormon                 7,594     948
Wh Other                 20,125     947
Wh Lutheran in Am        23,380     943
As Christn Reformed         298     943
Wh No Answer             44,397     942
Al U Methodist           26,037     939
Wh Afr Methodist            144     939
As Total                  70739     938* Asian Avg
Wh S Baptist Conv        14,165     938
Al Lutheran in Am        25,020     937
Wh Total                688,933     934* White Avg
As Lutheran in Am           471     931
As Un Church of Christ      253     930
Al S Baptist Conv        15,729     929
As Judaism                  218     925
Wh Christn Reformed       2,235     924
As Baptist                 3003     924
As Islam                   2184     923

And here's a 2002 report on high SAT scoring groups from Gene Expression: