Celtic Heroes

I have seen this question asked on multiple other threads and would like experienced mages to help settle this argument with actual verified data (not level 100 mage saying "imo blah blah blah"). I tested lvl 1 firebolt with and without skulls on training dummies, nonstop casting for 5 minutes and counting the number of casts I could squeeze into that timeframe, then repeated 5 times for each.
Here are my results:

Without skull- 38.4 casts/5min=7.68 casts per minute=7.81 secs between each firebolt (cooldown+cast time)
With skull- 45.8 casts/5min= 9.16 casts per minute=6.55 secs between each firebolt
There was a small amount of lag for every cast but it should affect both about the same so I'll ignore that for now.
(7.81-6.55)/7.81=.162

So including the cast time, which does not seem to be affected by skulls, I'm observing a total recast cooldown reduction of 16.2 percent, rather than 20
However, this 16 percent cooldown increases the total dps (neglecting boost with alternative mainhand when skull no equipped) by a factor of 9.16/7.68, or 19.3% higher dps.

Can anyone with a better fb skull or a fs skull run a similar procedure and post their results here?
I understand that there are several problems with using skulls, such as sigil timing in between fbs, reduced focus/firemagic leading to lower hits and more evasions, one skill being ready while the other is still casting which over time loses some dps, etc. But it is possible to stack up tons of firebolt/firestorm boosting gear that further amplifies the effect of the skull in comparison to a mordy grim.

I think u got 16.2% because u included cast time (which skulls dont reduce, only cooldown).

Id like to see a dps difference, with or without cast time (a reason to do it without is that skulls dont affect it, although that means it might not change and a reason to do it with cast time is the difference between cast times to fairly compare dps) between the two, I know firebolt is the biggest source of firemage's dps, but does this little cooldown reduction worth it over firestorm skull?

I dont lvl my mage currently so I wont be able to do this anytime soon, I hope Armo will take the burden on himself (be our hero Armo, all the ladies will swarm u ), and ofc eventually compare it to a grim.
Btw, someone compared once a skull to a grim (not same tier tho) and I think got slightly more dps from skull (like 5.1%), but I think some little detail was missing, and obviously its impossible to know how much does fire magic affect ur accuracy.

This varies too much depending on the gear a player has. If you have a lot of fire bolt boosting gear, choose fire bolt skull, if you don't then use grim or storm skull.

I would choose fire storm skull over grim because skill points for storm are really hard to come by and have to waste ring slots.

This varies too much depending on the gear a player has. If you have a lot of fire bolt boosting gear, choose fire bolt skull, if you don't then use grim or storm skull.

I would choose fire storm skull over grim because skill points for storm are really hard to come by and have to waste ring slots.

Besides rings and skull, is there any other item that adds firestorm? Although now due lvl 210 bumping max skill lvls its a bit less of a problem.

Hrung helms do also.

I use a +9 helm which lets me max the skill and not worry about using a ring slot.

Dark skull= 1 extra hit per 5 hits
Shadow skull= 1 extra hit per 4 hits
Void skull= 1 extra hit per 3.3 hits

Firebolt roughly 6 seconds cd so in a 15 min boss you have roughly 150 firebolts if cast time is removed from the equation so there for:
Dark skull= 30 extra fb hits per 15 mins
Shadow skull= 37.5 extra fb hits per 15 mins
Void skull= 45.45 extra fb hits per 15 mins

Firestorm roughly 16 seconds cd so in a 15 min boss fight you have roughly 56.25 firestorms if cast time is removed from the equation so there for:
Dark skull= 11.25 fs hits per 15 mins
Shadow skull= 14.06 fs hits per 15 mins
Void skull= 17.045 fs hits per 15 mins

If fb = 500 and fs =1000 (firestorm is roughly double firebolt in my experiences) then in a 15 min boss fight without a skull firebolt will deal 75,000 damage and firestorm will deal 56,250 damage, there for:
Dark skull= 90,000 fb dmg per 15 mins or 67,500 fs dmg per 15 mins
Shadow skull= 93,750 fb dmg per 15 mins or 70,310 fs dmg per 15 mins
Void skull= 97,725 fb dmg per 15 mins or 73,295 fs dmg per 15 mins

Ultimately which skull is better is based on gear (high direct dmg to firebolt then fb skull, high direct dmg to firestorm then fs skull) but In most situation fb skull out dps'a fs skull.

As for the grimore it is mostly based on gear. By the time you can use a grimore you will likely have a lot of focus and the focus to skull damage conversion slows down around 1800 focus in my experience it can be useful to swap focus to vit using the book increasing your survivability which decreases the odds of losing attunement therefor increasing dps by a good margin depending on how often you die during a boss fight. The grimore also adds fire/ice magic which can increase overall damage of all skills by a small margin thus increasing dps. The biggest factor of the ice/fire magic added by the book is that it will increase the rate at which your skills hit, mages as of right now have very high evasion rate therefor the the increase in skill hit chance can make it better than either skull.

Overall it comes down to gear:
High survivability/high fire/ice magic use skull for sure
Low survivability/low ice/firemagic use grimore

Of course there is also a certain amount of personal preference involved and you may use grimore over skull or fs skull over fb skull. Imo mage is one of the most diverse classes and can support support a variety of play styles so in the end use the gear that best suits you.

Ps. I may have got the cd times on the skills wrong, if so please tell me and I will fix it.

I think fire bolt is 7 seconds, fire storm 15 seconds. My bolt and storm are only like 600 damage apart so bolt skull is ridiculously better than storm in my case.

This varies too much depending on the gear a player has. If you have a lot of fire bolt boosting gear, choose fire bolt skull, if you don't then use grim or storm skull.

I would choose fire storm skull over grim because skill points for storm are really hard to come by and have to waste ring slots.

Besides rings and skull, is there any other item that adds firestorm? Although now due lvl 210 bumping max skill lvls its a bit less of a problem.

Alchemical/occult boots add to firestorm dmg

^I meant skill lvls and Armo answered but thanks