Yes, the Hebrews always believed that the sixth letter was involved in the creation of the world. Yes, there were a number of interesting traditions related to the 'sixthness' of the universe but one thing I always overlooked - and it is very important when considering the Alexandrian Church. The Hebrew lunar calendar has 354 days; the Alexandrian Church shifted to a 360 calendar (cf. Clement Strom.i.24). In other words, six days were added to the traditional calendar of the Jews or as we see in Maimonides:
By how much does the solar year exceed the lunar year? By approximately 11 days. Therefore, whenever this excess accumulates to about 30 days, or a little more or less, one month is added and the particular year is made to consist of 13 months, and this is the so-called embolismic (intercalated) year. For the year could not consist of twelve months plus so-and-so many days, since it is said: throughout the months of the year (Num 28:14), which implies that we should count the year by months and not by days.[Maimonides Mishneh Torah Sanctification of the New Moon Translated from the Hebrew by Solomon Gandz, Yale Judaica Series, Volume 11, New Haven: Yale University Press, 1956]
The 11 day difference between the 'full' 365 day solar calendar becomes six when the five epagomenes are subtracted.