do 20/20 upgrades stack?

I want to get two of the collector items from teh desert and snow area, each have 20/20 buffs. One is a healing anch, one is a rod or cane.

My question is, if i put on two items, each wiht a 20/20 buff, does that make it 40/40, assuming they increase the same thing?

I don't believe there is a 20/20 rod of any type but yes they do stack to 20/40 if you use the collector items. Rather, more accurately, they stack to 20% of 20% of the recast time

Yes they do stack, how exactly i'm not sure, maybe one day i should play around with that.