Here's my set-up for testing if damage amplifiers stack:
Regular divination wand: 38-71 damage, 1.4 attacks per second
+37 minimum damage from rings/amulet
casting fire hydra w/ immolation (10% damage done to targets hit by fire for 3 seconds)
casting slow time w/ time warp glyph (20% damage done to enemies in the slow)
ray of frost w/ useless glyph (215% weapon damage)
shooting at nightmare mode Siegebreaker
My weapon damage should be 75 no matter what. 215% of 75 is 161.25. Add on the bonus damage from my int (+547%) to reach 1043.2875 damage per tick of ray of frost. With just slow time I should expect to do 1251.945 per tick. With just fire hydra I expect to do 1147.61625 per tick. With both stacking multiplicatively I expect to do 1377.1395.
Actual damage numbers:
803 w/ immolation
876 w/ time warp
949 w/ immolation and time warp
The numbers are lower than I expected, probably because Siegebreaker has armor/resistances. I couldn't find any specific values datamined from anywhere yet so I can't verify that. At any rate, the numbers do show some very clear stats. 803 is 10% more than 730. 876 is 20% more than 730. 949 is 30% more than 730. Clearly the damage amplifiers stack additively.
Now for a preliminary look at attack speed:
disintegrate w/ useless glyph (155% weapon damage)
shooting at normal Ghom
Regular two handed-mace: 22-23 damage, .9 attacks per second
Regular dagger: 7-20 damage, 1.5 attacks per second
Regular mace w/ 10% attack speed gloves: .99 attacks per second
Regular dagger w/ 10% attack speed gloves: 1.65 attacks per second
The test here is going to be how much damage I can do in a full arcane power bar.
2447 (22 ticks, 111 per tick)
939 (8 ticks, 117 per tick)
2021 (18 ticks, 112 per tick)
1081 (8 ticks, 135 per tick)
With 100 base arcane power and 10 regeneration per second I need to consider how long it should take to run out. I spend 20 per 'cast' of disintegrate. I need to find the point where 100+10x=20xy where y is the number of attacks per second.
y=.9, 100+10x=18x, x=12.5
y=1.5, 100+10x=30x, x=5
y=.99, 100+10x=19.8x, x=10.2
y=1.65, 100+10x=33x, x=4.35
Ok, not really sure what's going on here anymore. Part of the problem is going to be that I'm pretty much just guessing when I'm completely out of arcane power. I didn't want to melee attack... Maybe I need to find a stationary target? Who could that be? The really interesting thing, to me, is that the tick period isn't directly related to the speed of my weapon. I was expecting the dagger to tick more frequently for less damage and to run me out of arcane power quicker. It certainly ran me out of arcane power in a real hurry but the damage numbers didn't seem to pop up more frequently and they weren't smaller. In fact if I had to guess what was going on I'd say disintegrate ticks 1.75 times per second and it just sort of keeps track of how much damage 'should' have been done in that period of time based on your listed DPS.
I went to act 3 nightmare and shot at some of the demonic ballistaes (after clearing the zone around them) to calculate total damage done from a full arcane power bar. I couldn't manage to get the damage ticks on the screen but I am confident I used the full bar until I ran out and never meleed the monster. Using the estimated number of seconds from above I will also show DPS numbers:
mace: 2233, 179DPS
dagger: 938, 188 DPS
mace+gloves: 2134, 209DPS
dagger+gloves: 827, 190DPS
Now there's going to be an issue with these weapons having actual damage ranges (especially the dagger) and having a very small sample size. I wish there was a combat log of some kind so I could just unload into enemies for a while and then have real numbers. One thing to keep in mind as well is I can cast my 'signature' spell while out of arcane power, that the dagger didn't get to use as much arcane power because it ran out faster and I didn't keep going when some regenerated, and that in real fights you have to run around which is free regen time.
One thing's for sure... Attack speed on my weapon doesn't do anything like what I would have thought for disintegrate.
How about damage? I have a +7-14 damage ring. Let's see how it impacts the mace and dagger against the ballistae.
mace - 23 ticks, 3934 damage, 315DPS
dagger - 9 ticks, 2057 damage, 411DPS
This time I managed to find a spot where I could count the ticks. I've also been noticing (something I actually notice a lot while playing the game) that the first and last ticks tend to do less damage than a normal tick. I think the game probably has a precise clock cycle where it checks to see how much damage was done in the last .5 seconds and displays that much as a scrolling combat text number. It's pretty clear here that adding extra damage is more impactful with a faster weapon. Even my character sheet agrees. It lists identical damage numbers with just the two weapons equipped and shows a bigger number for the faster weapon once I equip the ring.
The slower weapon is better in terms of arcane power usage. The faster weapon is better in terms of making use of flat bonus damage. At least with this once spell, anyway. I really need to mock up a couple builds and take into account the damage of my signature spells...