I found this website on tablecloth sizing and, according to it, the standard drop for round tables is 15". So, the 90" tablecloths should be fine for 72" tables. (This page actually recommends 120" tablecloths for 72" round tables! I'd probably go with 90", though, for church tables.)
http://www.ebay.com/gds/Tablecloth-s...6614159/g.html