This page has all of the item properties and their caps per item and total:
http://uo.stratics.com/content/arms-...properties.php

According to that page, for damage increase, each jewelry piece can have a max DI of 25 and each weapon can have a max DI of 50, with your total allowable on your character of 100. Anything above 100 won't help you. Might as well dump those extra points into something else, like DCI.