"Old Beleiverism was a move away from liturgical unity, as had been occuring in the Orthodox Church for the past 1500 years as more and more local usages died out and were replaced with new ones--yes, new ones, as the Neo-Sabbaitic synthesis was an amalgamation of monastic and cathedral rites--these folks jumped ship at a time when Orthodox were moving closer together. The Old Calendarists, on the other hand, are those who resisted a change away from Orthodox unity (unity not being limited solely to the present time)."
You are using the "Nikonian argument" but fail to see things from their perspective. During the reign of Tsar Ivan IV, there was the Stoglav (Hundred Chapters) Council, which addressed the issue of the liturgical differences between the Greek and Russian Churches. At that council, it was decreed that the Russian usuage was the same as had been taught to them by their Greek baptizers. The Old Believers also uphold the memory of Saint Maximus the Greek, who affirmed this. The OB explanation for the liturgical and textual differences lie in the fact that the Turks forbade the Greeks to publish books, so the Church had all their liturgical books printed in Venice and Paris by Jesuits. Similar to the argument for using the Septuagint Greek OT as opposed to the Hebrew Massoretic, the OB maintain that their Slavonic texts are more authentic because they are not tamped with by Jesuits.
The irony of all this is that the further development of the Russian practice westernized it to such a degree that the Old Rite, to me, seems closer to the traditional Greek usuage than the current Russian practice. Interestingly enough, there was a book in Russian writen about the history of Slavonic translations which pointed out that in the late 19th century the Holy Synod did make some textual changes, often restoring Pre-Nikonian texts.
I think we cannot ignore the similarities between the Old Believers and the Old Calendarists. On the positive side, there is great love for the faith and liturgical worship. Their faithful are much better trained in apologetics than the rest of us. One of the distinctive characteristics about the OBs before the Revolution was that there was a higher rate of literacy among them and thus they often had better skills in rhetoric than village priests of the official Russian Church.
In both cases, recent councils had affirmed their main cause of contingency with the official church. I noted the Stoglav council and its upholding of the Russian rites. Our Old Calendarist friends often site local councils and Patriarchal epistles and tomes concerning baptism and the Church Calendar. Secondly, in both cases the changes were done in a very unpastoral manner and enforced in a rather Papal manner. Thirdly, both groups experienced terrible persecution at the onset of their resistance to changes.
However, both groups have divided into manner small splinter groups that usually do not recognize one another. In the case of the OBs, it got to the point where there were priestless groups, sects that practiced flagulation, even groups that practices castration. There was one group that split off called the Molokhany (Moloko means milk in Russian), who believed that milk can be drunk during fasting times. Among the Old Calendarists, they are divided about grace in the official church. Furthermore, they argue when that grace was lost. Then there are divisions over the Old Man Trinity Icon and I am certain there are divisions caused by ego clashes.
As for the "official" Church, these problems persist. After the 17th century, the Russian Church became more and more Westernized. Peter the Great abolished the patriarchate in favor of a Holy Synod, based on the Swedish Lutheran Church. During Catherine the Great's reign, Western art and music crept into the Russian Church. In the seminaries, Summa Theologica became the standard textbook used. Furthermore, after the 17th century we see Chrismation eventually become the norm for accepting converts and in Ukraine, pouring became a form used for baptism.
I don't think it necessary to chronicle what happened in the "official" churches in the 20th century. However, despite all these problems, grace remained that saints sprang forth. In Russia, we have Saint Paisius Velichkovsky, the Optina Elders, Saint Ignatius Brianchaninov, Saint Theophan the Recluse, Saint Tikhon of Zadonsk, Saint Seraphim of Sarov, Saint Philaret of Moscow, all of whom lived in the 18th and 19th centuries.
In the Greek Church, we have saints such as Saint Nicholas Planas. I am currently reading "Precious Vessels of the Holy Spirit", which is about contemporary Greek Elders, many of whom lived through the calendar changes, others were born afterwards, but still led holy lives and became grace bearing elders.
Edward Henderson
. Although I will say, it would be cool to go to the ROCOR Old Believer parish in PA someday to experience what it used to be like in Russia centuries ago.