Four Ums or perfect resist all jewels would give 60% resist all, the most possible on any armour AFAIK. However, this is really a tremendous waste. A Smoke armour has just 50% resist all, but has other boni, and is so much cheaper.

And I want the Griswold armour for the empty sockets. Some nice lightning damage jewels would let my bowasorc deal a lot more damage. If I wanted a resistance armour, I'd just use something else ;) .