What christian/surnames are you looking for?

The earliest records on FOD is 1538 (98 entries)

The Gloucester Marriage Index have a few back to 1625.

The Church of Latter Day Saints site is also very useful

as is the Gloucestershire Records Office Database (including Wills from 1541)

http://www.gloucestershire.gov.uk/archives

Earlier records are sometimes written in Latin - as in my 'family records' - and I used paid Researchers to search Gloucestershire/Wiltshire/Berkshire Records Office for these documents.

Also not forgetting exchange of information with fellow researchers via various websites.