Looking at this profile, it's clear it's been subject to a lot of research and hard work. I've read Marjorie Snelling's piece on Snelling, which is a terrific piece of investigative work that is direct, detailed, and well-reasoned. I can volunteer a few ideas, but these come from a few hours of research, unlike the other folks who have been working on this profile for ages!
For starters, I'd volunteer the possibility that John Snelling, baptized at Southwark, St. Saviour's, Surrey on 13 Mar 1630 could be a viable record (FindMyPast). Some research on the church/parish reveals that Saint Mary Overie was an Augustinian priory, from 1106 to 1538. After Henry VIII's dissolution of the monasteries, it became the Church of St. Saviour's. So for all intents and purposes, St. Saviour's and Saint Mary Overie's are the same church serving the same parish.
The above record shows his father's name as "Nicholas", and his profession as "waterman". Considering the fact that John seems to have stuck to the trades and worked with his hands, I find this fairly possible that he inherited those class and social inclinations from his father.
Marjorie Snelling references John Snelling giving his age in 1671 as '"forty-three years of thereabouts," resulting in a birth year of approximately 1628.' Being baptized in 1630, I also find it possible that it would be closer to Marjorie's conclusions around his age, and with Surrey as a birthplace, to her suggestions as to this Snelling's origins.
A perusal of the burial records doesn't show a conclusive burial record for the John I'm suggesting in the Southwark area, but there is a marriage record that could possibly put him out of contention for Snelling-5. The banns for the marriage of John Snelling and Mary Snelling were read on 8 May 1656, both of the parish of Southwark, St. Olave, Surrey (FMP). This could suggest that the John Snelling in the baptismal record above stayed in Southwark and married a relative in an nearby parish. St. Olave is very close to, if not adjacent to St. Saviour's parish in Southwark.
On the other hand, since Snelling-5 is in Maine by 1655, according to Marjorie Snelling, it's also possible that marriage pertains to a different baptismal record entirely.
TLDR: I would volunteer that this baptismal record is what seems like the best fit to me for Snelling-5, keeping in mind that my research has not been exhaustive and I've been more focused on the study of Devon records, rather than Surrey ones. (That being said, I might have to make a switch. All those Surrey wills have the texts transcribed in the Find My Past records! What a boon!) My suggestion comes with the cautions above.
