Please, for the love of god, donât listen to people telling you to go fast offhand.
For combat:
Your off-hand speed is largely irrelevant. A slower & hard hitting off-hand is actually, arguably, better in all areas. This can be a pita in pvp for poison application, but combat was gimmicky-at-best in pvp back in vanilla.
For assassination:
Your off-hand speed is largely irrelevant. A slower off hand is actually, arguably, better outside of pvp.
Why:
There were two things which influenced the development of the âfast off-handâ rogue preference.
For combat, there was Combat Potency. A talent which regenned energy on off-hand hit. i canât remember if the original implementation was 5 per hit, or a chance to proc for 20, as both iterations have existed throughout the game. This was a talent implemented in BC.
For assassination (and actually combat as well), there was the removal of debuff slots. Vanilla wow originally had a 8 debuff per mob limit, and later on a 16 debuff per mob limit. That meant that, in a raid of 40 people, less than half of the raid could put a SINGLE debuff onto the boss⌠At the best of times. The current tank took up 3 of those debuff slots with Sunder Armor, T-clap, and Demo-shout. The rest were âreservedâ for utility usage. For example: Shadow priests needed two (mind-flay was a debuff based attack) not because they were top-tier dps, but because they were mana batteries for the healers. Suffice it to say that rogue Deadly Poison wasnât high on the priority list, and poisons didnât actually do much damage in classic. Not to mention a not insubstantial amount of mobs were flat-out immune.
This changed in BC, when they removed the debuff limit.
So, where did that leave rogues?
Well, it left them using instant poison. Which was a pretty negligible damage source even before you got into the issues with small amounts of hit on gear, and massive off-hand hit / parry / glancing / the % hit chance on rogue gear not effecting poisons (poisons were âmagicalâ hits). Really the only thing you should care about for your off-hand is going to be stats. That being agi, raw dps, bonuses (+% to crit or hit), and procs. Speed is about the least important factor.
This is even more true for combat swords. The 5% double swing massively out damages any minuscule benefit from poisons, so itâs much better to shove a beefy slow weapon into your OH and go to town. Traditional combat swords ran stuff like double Skullforged Reaver, or Chromo Temp + Maladath.
EDIT:
An important explanation: Weapon speed is hugely important for your MH weapon, even more so than the actual DPS.
This is because, back in vanilla, % damage increase abilities (Backstab, SS, Hemo) scaled with the speed of your mainhand. Basically theyâd amp up the % scaling behind the scenes for uniquely slow weapons, and reduce the % scaling for uniquely fast ones. This was why some blue & green weapons (daggers with 2.0 swing speed and such) were actually better than epic items. And also why Hemo became absolutely nightmarish with that Spare Part mace from Naxx.