The Thrill of the Spreadsheet: Opening with Glaive Toss

Lately, there's been a bit of discussion about whether or not it's actually beneficial to use Glaive Toss as the opener in your rotation.   I thought it might be fun to go through some of the pros and cons.

In Favor of Glaives to Open:

• Glaives has a slow travel time, so at 40 yards from the boss, you can cast it 2 seconds before the pull, giving you an "extra" shot.   
• You can proc trinkets from "casting" glaives,  and then get the benefit of the proc a couple seconds later when it actually hits the target.  
• Due again to the slow travel speed and low focus cost (15 focus), you can precast Glaives and be back to full focus by the time you're officially pulling.

Against a Glaives Opener:

• Glaives is a fairly powerful shot,  and since it scales purely with Ranged Attack Power, it benefits more from your procs than shots like Arcane Shot (which is based mostly on Weapon Damage, which RAP only slightly modifies).   Therefor you should save it for after your procs are up.  
• You can never really trust a tank to pull right on the timer, so if you're saving your MD for adds or something other than the boss  opener, you could risk pulling agro and dying, which tends to have an adverse affect on DPS.   

Proponents:
Going through the top parses, it seems that most heroic raiding hunters are opening single target fights with Glaive Toss.   I imagine this is primarily due to being able to pre-cast it.   However, on the Cloak and Quiver a few weeks ago,  Solar was talking about an alternative: pre-casting Cobra Shot, which doesn't do much damage, so you don't care too much about it getting the benefit of your procs, and has the added benefit of not costing focus, so you can use it to proc your trinkets, and still have 100 (or 120) focus when your start your initial burst).   The downside is you can't completely precast it, because it begins AutoShot, so you can only begin to cast it 1 second before pull (which will cause any autoshots to not hit until the countdown reaches pull).

Context:
The biggest argument against using GT as an opener is that you're not getting the benefit on it from your procs.   So let's look at some different numbers.   Each Glaive does the following damage against it's primary target:

GT Damage = (.2RAP+{437:1308})*4

An average geared raider, with buffs, flasks, etc, will have about 100,000 AP,  which is a nice round number, so we'll use that as our basis.   That means without any procs, our Glaive Toss should do 83488 damage per Glaive for a normal hit (not crit).   However, this is physical damage, so we'll also need to consider armor.   An average level 93 boss will have about 24835 damage, which will end up reducing physical damage by about 30%.  That puts our average damage per glaive at about 58,568.5.   This could also be affected by Multi-strike, but that won't be significant enough to concern us for now.

My Haromm's Trinket (which is Heroic WF with 4 upgrades) has a proc of 16,295 agility, my AoC proc adds 15409 agility, Juice adds another 4000 and the scope 1800, bringing us up to a total RAP while all are proc'ed of 218,218, a huge 128,272 RAP increase.   Using the same formula, that brings our ave. hit for each GT to 133,796, which is definitely significant; remember these are for one glaive, you'll get 2 each time you cast GT.

To know what that means, we need to compare it to something. For me, with a Heroic, non-WF weapon, arcane averages about 85,783 for normal hits, with no procs.   With all of those procs up, arcane is averaging   124842.

That means using your GT while all your procs are up nets you an extra 150,453, while using arcane with all your procs up only nets you an additional 39,059 damage.   It's starting to sound like saving GT is pretty significant.

What to do:
The fun part about procs, is we just don't know when they'll arrive.   It could be that you precast GT and 15 seconds later, all of your procs are up so you'll still get that huge benefit from them.   Or,  it could be that you miss out on it so you lose that damage.

In either of those cases, the cobra shot opener is definitely safer.   But then there's another cost we haven't looked at; when precasting GT, it's basically just free damage.  That is to say, you're adding an extra GCD to your fight.

Unfortunately, there's no good mathematical model that's going to answer this one, as both sides have pretty strong arguments.   You definitely do get a huge boost from saving GT for when your procs are up, and you definitely do get an entire extra GCD by pre-casting it.

Hopefully this will help in weighing the pros and cons of the Glaive Toss opener, though.  On the next Thrill of the Spreadsheet, I'm going to be looking at the pros and cons of the second most common opening shot, Serpent Sting.