Weapon speed in damage calc'sFollow

Since your post exhibits some degree of intelligence and actual prior research (except you still didn't check the FAQ), I will answer without flaming you.

Slow main hand is an anachronism, its misleading for new players (aka players after 1.7), because of two reasons, one those players don't understand what why weapon speeds were (and to some degree still) important in damage calculations, two they may not understand normalization and how it affects them.

For the main hand, when people state slow weapons they mean a weapon with higher high end damage, in other words slower and harder hitting weapons which is typically the case with how Blizzard creates items. This is especially important because of the various instant cast skills we have as Rogues that depend on the main hand damage, Sinister Strike is a primary example of this; a slower harder hitting weapon will result in a larger Sinister Strike damage.

Now a little history to put it in perspective, before 1.7 patch, there were a handful weapons that were clearly better than the others mainly due to their weapon speed, Barman Shanker is one of these. The reason for this is that in the damage calculation algorithm, you have a weapon speed multiplier in which your damage values are multiplied by the weapon speed, see the benefits?

Blizzard wanted to fix this major itemization issue in 1.7 and I think 1.9 for Ranged Weapons and did so by normalizing all the weapon multipliers to a static value unique to each class of weapons, 1H Swords, Daggers, etc.. In other words weapon speed no longer matters in your main hand DPS, your weapon's damage range is far more important in this regard....except in one special case for Rogues: Hemorrage. Hemo (compared to Sinister Strike) is not normalized therefore pre-1.7 knowledge still applies and weapon speed is still very much a factor.

Now for your off-hand, your weapon speed matters very much as poison procs, Combat Potency procs play an important part in raising your DPS, so faster weapons are favored here.

Finally, I'll give you an example to help you out, speaking strictly of damage and nothing else (stats/ratings/etc) on the weapon, if you have 2 potential main hand swords, one is 2.7 and the other 2.8 speed, instead of focusing on the DPS rating or the weapon speed, you need to look at the damage range and find the mean/median damage the weapon puts out, the one with the higher value is the one you want to use in your main hand. Same applies to maces, fists, daggers.