Stacking Bonuses

It's time once again for Jade's n00b wuestion of the month. Now I realize that if I have a weapon and an off hand that each add + to health, they stack. (ie. +20 +20 = 40) But let's say that I have a weapon that has "enchantments last 20% longer" and an off hand with the same mod (dunno if it's possible but it's just and example). Will enchantments last 40% longer? Do all "same type of bonuses" stack for weapon and offhand? (It takes me a while to get to the point but I do get there eventually! )

We just discussed this recently with Improved skill recharge. What we determined in that thread is that with 20% skill recharge and 20% skill recharge, it stacks to 36%. Actually I believe it was 32% fast and 4% super fast, but total 36% chance of improved skill recharge. I'd guess it would be the same for enchantments lasting longer, but I'm not positive.

Strange how it wouldn't be 40%. But I guess if it was, then people would be out there tryin to get things that would stack as close to 100% as possible.