I have now completed extracting the VICKERY births index 1837 to 1899. In total there were 4620 entries compared to 1432 for VICARY and other derivatives in the same period.
In doing this exercise I gain the impression that the Vickery clan started moving away from Devon and Somerset in greater numbers, earlier, and to greater distances than the Vicary clan. This might be because coming predominantly from Somerset they were closer to main roads, railways, etc..
The reason it has taken me longer than expected to complete this task is that the London Metropolitan Archives went on line after Christmas and I have also extracted all the VICARY entries from there.
Please feel free to contact me if you want me to look up any Vicary or Vickery name, you never know, I might just have a family tree connecting to yours.