You are very close to territory that will make some hydrangeas not bloom, chefhick. Macrophyllas may have a hard time in cold zones and require winter protection. Do you have a picture -even an old one- of the shrubs in bloom? It might help determine the variety.

Until that is determined, I suggest pruning only if needed. And only prune (1) after the plant blooms but (2) before August. Then apply winter protection techniques as soon as the plants go dormant (the leaves dry out, etc) in the Fall. See the link below.

Here is a link that might be useful: Overwintering Hydrangea macrophylla winter protection

I don't have any photos of the plants. But I swear they looked like these I found on the web. They seem more flat and less like the ball shaped varieties.
I could be mistaken but this photo is very close. Thanks for the info. I think the plants were good to zone 5. I don't think winter chill is an issue.

Here is a link that might be useful: http://www.pbase.com/cmf46/image/98526712