Synergy Proc (Pure damage)
Goren Trinket (Roughly 20% crit, depending on version)
Ring Proc (Intellect)
Weapon Proc (Mastery)
For Destruction you aren't using Synergy, so Goren becomes #1 (it would still be first even with Synergy, ~20% vs only 15%).
Keep in mind that a there is a small window where you can delay to try for some extra procs, for example on a 15 second proc, you've got a good 5-6 seconds where you can 'delay' waiting for a second proc or trinket before sending out Demonbolts. With weapon proc having 40-50% up-time, there's a good chance that delaying for that small window will allow it to proc (along with trinket/ring if you are lucky).
When it comes to multiple procs being up, or one that might fade mid way through your Demonbolts - it's fairly difficult to determine what situation is 'optimal' and if you should start casting right away, or if you let the proc drop hoping for something else to refresh. Hopefully someone better at math then me could chime in on how to calculate that sort of situation.
In demo, I find that waiting for procs to blow off big hits is dps loss, cause DB takes so long to get 4 off
In affliction can't time it aswell, as you need to have 4 shards when DK cd is up.
Only in destro can get off 1 or two chaos bolts with procs as DK does not always line up with 4 chaos bolts and it ont takes 2.5 sec to get one off so you are garenteed to get the big hit spell of with the procs
Obviously you can't wait too long, but the Synergy proc really is massive - and waiting an few extra seconds while building fury to 900'ish (instead of going right into Metamorph at 800) on average will definitely increase your damage.