Guild Wars 2

This is a general question I had recently!

I play a thief with 30 points into the one tree, which gives me 30% base condition duration up. Ontop of that, I have +15% bleedpoison duration up from my armor.

Tonight, I made two “Giving” daggers, which are each +10% duration up. Does anyone know if these stack in with the rest of it all?

Also, I was curious if anyone could tell me what the 6 sigil bonus for “Afflicted” set does. It says "(6): Create a death nova when you go down. ". I assume that means when I’m downed, some sort of aoe triggers. But, what is it? Does it do fairly good damage? Does it justify the 6th bonus? (I was considering getting 2 set bonus on another one for another +10% condition duration.)

This is the Death Nova in question:

http://wiki.guildwars2.com/wiki/Death_Nova