Some thoughts about the uberland that have been post in this great 290+ pages thread:
1) You need stacked resists when fighting Mephisto: 300 is the number: 100 hell + 125 conviction + 75 to get max. Lightning is the most dangerous by far, so Tgods is always a good idea (but you'll need 310 light that way...

).
2) You need life tap: You can't leech from Mephisto and his skellies (and, not sure, just a bit from Diablo and Baal). Besides, life leech doesn't work with smite and you'd have a hard time hitting them with other skill. Sometimes, my red bulb went from 100% to less than 10% and back in 1 second... If you don't want Dracs, you can use a wand with life tap charges. Just remember slvl 3 life tap lasts around 30seconds, so you have to be fast...
3) You need crushing blow: To drop good amount of the Ubers life at the beginning of the fight. Good damaging weapons would help only at the end
4) You need open wounds: To stop the life regeneration of the Ubers, or you will have a hard time taking the last sliver of their lives.
For weapon, you could use a double shaeled Heaven's Light and still have good results.
For armor, Chains of Honor are better than Fortitude for this task.
By the way, if you have 4pdiamonds in your shield, it's base resists should be 15, not a very good base for a runeword one, but pretty high like it is.