Regarding information from burials, I have found a bit more about the Wilstead lot. I located - and John has confirmed from the PRs - a Thomas Armstrong married to Christian Fiddes, and a John Armstrong married to an Edith, who were producing children in the 1750-1770 period.
Having turned up a burial for a Sarah Armstrong w/o William in Sep 1752, I then found a burial for a William in Sep 1765. And a baptism for Thomas son of William and Sarah, on 21 Apr 1734. These all came from Ancestry's Bedfordshire Parish and Probate records, which has a sizeable chunk of the Wilstead parish records.
The FHO pay-per-view website has what looks like all of the NBI for Bedfordshire, and the burials mentioned above are all there.
So we have a William and a Sarah, who married somewhere, and moved to Wilstead before 1734, possibly with at least one child named John. In 1734 they had a son named Thomas.
Sarah died and was buried 26 Sep 1752. William MAY have died in Sep 1765 - but this burial could have been that of the son of John and Edith b 1754, as no age is given.
Thomas married Christian Fiddes in 1766 - they had two sons, Thomas b 1766 and William b 1769.
John married Edith - perhaps Edy Grange from Houghton Conquest in 1753 - and produced William b 1754 and John b 1760.
I then found two burials in Maulden -
Eddey ARMSTRONG Date 3 Jan 1770 Aged – Place Maulden Description St Mary Denomination Anglican County code BDF
John ARMSTRONG Date 9 Nov 1773 Aged – Place Maulden Description St Mary Denomination Anglican County code BDF
Sadly no age is given to help determine whether these are the parents of John b 1760-ish in Wilstead. They died quite young if they are - both only in their 40s or 50s.
Amongst all the other burials for John Armstrongs, there is really only one that can be linked to John b 1760, son of John and Edith, and that's John Armstrong, buried in Ravensden in 1826 aged 66.
A John Armstrong was buried in Wilstead in 1872 aged 73 - he is most likely to have been the son of William Armstrong and Mary, who began producing children in 1800, with John as their eldest. William could have been either the son of Thomas and Christian or the son of John and Edith. I favour the son of Thomas and Christian, purely because of age!
All highly circumstantial, of course, but worth pursuing...?