Guild Wars 2

I have a level 80 thief and I made a build with 16k hp, 2050 power and 57% critical chance. I have to choose between Sigil of bloodlust to have 2300 power or sigil of perception to have 70% critical chance. P.S.: I’m a backstab thief.

Get bloodlust and spec for hidden killer

57% crit chance is borderline overkill. Keep in mind with many traits (which you should take) you’ll have a high upkeep of Fury, which gives you another 20% crit chance. And 90% crit chance is useless compared to more power.

http://gw2skills.net/editor/?fYAQNAoYVlUmiO3cy9E/5Ey2jeqCJKuHGlT1UdFuKA-TsAg0CnIeS9k7JzTynsPNsYZxsAA

Gonna leave this here, this is for everything actually. Note pvp I use DD DP, as for WvW I go with zerk trinkets, other than that everything is pretty much across all game modes, cept sigil of ifre on dagger, I use air in pvp. It looks like a build you were going for, but I dont know your weapon preference or playstyle as this build is very stealth heavy. SoS is often switched with blinding powder

Oh, and the armor is valkyrie, all valk

all ascended zerker trinkets, (power,tough,vit) head and Coat, Valkyre Shoulder and gloves, Zerker Leggings, Boots

Power increase:
(oldpower + addedpower) / (oldpower) =1.XXYYYY
XX.YYY%= %damage increase

Precision increase:
21 precision = +1% Crit chance at level 80.
Added Precision / 21 = X.YYY
X = addedcritchance
(1 + ((.5 + critdamage) * (oldcritchance + addedcritchance))) / (1 + (.5 + critdamage) * oldcritchance) =1.XXYYY
XX.YYY= %damage increase

Add your stats where needed and you can see which is better. I’d do it for you, but you didnt list your crit damage or exact precision.

For examples and more math and math about why using soldiers and berserkers is superior to valk and berserkers for survivability and damage see this thread:
https://forum-en.gw2archive.eu/forum/professions/thief/Building-a-better-D-D-thief/page/3#post2615780