Is there a maximum amount of effective dr? For instance, will only say...30% work...anything after that is non-effective...or as long as you keep putting it on, it keeps adding and working...so if you could get to 100% you would never take damage?
If you are trying to reduce the physical damage taken, I suggest a mixture of both - damage taken and % damage reduce. The - damage works very well on the minor monsters in large groups. The % damage reduce works better on champions or mini-bosses like The Smith or boss packs that are fanat/extra strong.
Say you are going against a monster that does 100 points of physical damage.
With max % damage reduce gear, you can only get the damage to 50 per hit...
if you have.. say -50 damage taken(not hard to get) as well as 50% damage reduce, you can reduce your total damage to 25 per hit