The approximate formula:
(Base Str * 1.632 + Extra Str * 1.5058) * Buff Rate = Attack
Base Str - the Str you have without any equips on.
Extra Str - the Str you gain additionally with equips. This can be shown in the display menu when highlighting "Str".
What does this mean?
1. Contrary to many skill descriptions that state attack will be increased by a percentage of current attack, this is a close approximation of the actual formula used to determine the additional attack. Simply put, THE DESCRIPTIONS ARE WRONG
*The only exception in the warrior tree is Annihilation, which works properly however only increases the damage on the first monster hit.
2. "Str" is the main attribute that affects the return of these attack buffs. For this reason, Grizzly Power is the only stackable buff because it adds an additional 25 Str. Every other buff(i.e. God of Wrath, Advance Sword Mastery, and Wild Rage) is calculated independently because they DO NOT rely on "Atk", but rather Str.
3. The weapon your using, unless it has a Str option, DOES NOT impact the gain from those buffs.
So why should you care?... Because your character will be a lot weaker than expected and you will probably waste valuable SP on bad skills!
Here's a true example.
A level 48 myrmidon has a total of 128 base Strength. At this level, he can have:
Lvl 3 Bloody Roar -100% Buff Rate
Lvl 5 Gamble's God of Wrath - 30% Buff Rate
Lvl 5 Grizzly Power - +25 Str and 15% Buff Rate
Lvl 5 Advance Sword Mastery - 21% Buff Rate
Lvl 2 Wild Rage - 10% Buff Rate
Total: 1.76 Buff Rate
Note: I used "buff rate" instead of percentage increase in attack to make things clearer.
Now with all five Buffs on and the level 47 Spiral Set which adds an additional 25 Str, you have these results:
Base Str: 128
Extra Str: 50
Attack gained from each Buff: (rounded)
Bloody Roar- 284
God of Wrath- 85
Grizzly Power- 86 (43 from buff + 43 from 25 Str)
Advance Sword Mastery- 60
Wild Rage- 28
Now to obtain that 500 attack, this person used a total of 370 SP. Seems rather inefficient if this person had instead decided to use sword mastery and sharpness blade(fixed attack additions)- he would have 335 additional attack for 105 SP. To put this in perspective, lets look at the ratios:
Ratios of Atk to SP:
Bloody Roar: 3.16
God of Wrath: .85
Grizzly Power: 1.147
Advance Sword Mastery: .8
Wild Rage: .93
Sword Mastery: .93
Sharpness Blade: 5.78
In this example, definite keepers are Bloody Roar, Grizzly Power, and Sharpness Blade. While originally Sword Mastery did look useful, the skill points may be more useful allocated into an attack skill instead. Remember also that Wild Rage, Advance Sword Mastery, and God of Wrath will improve with the addition of more Str, and each Str adds around 1.7 to 1.8 more attack on its own merit. So depending on your Base Str and Extra Str, certain skills will be a better investment than others. Unfortunately since buffs are based on Str. and the multipliers are so low, it could also be a better investment to raise the attack level of skills, not buffs.
Feel free to use this information to figure it out and hope you enjoyed the read ^^.
Here's also the link to my data compilation if your extremely bored:http://dragonica.mmosite.com/content/2009-09-04/20090904220643050.shtml
Lvl : Base Str
29 : 67
31 : 71
48 : 128
45 : 98