Consider the following scenarios for multi-hit WS:
Low Accuracy, Low Attack (relative to what you are fighting)
Results in an inconsistent WS damage and overall low WS average.
High Accuracy, Low Attack (relative to what you are fighting)
Results in a consistent WS damage, but low WS average.
Low Accuracy, High Attack (relative to what you are fighting)
Results in a inconsistent WS damage. Damage will spike radically depending on how many hits land.
High Accuracy, High Attack (relative to what you are fighting)
Results in a consistent WS damage, and overall moderate to high WS average.
To get more consistent results from multi-hit WSs, the most important factor is having enough Accuracy to land all the hits. Now accuracy alone will only net you more consistent WS damage. To determine if your WS damage will be low, moderate, or high primarily depends on the defense/VIT rating of the mob you are fighting.
I know you were asking about WS Modifiers, but based on my experience, you will see more net gain from gearing Accuracy and Attack then piling on DEX and STR. But to answer your Dancing Edge question more directly, it would be silly to sacrifice STR for CHR. STR also increases your overall attack (though a relatively small boost) as well as other effects such as the ones Tagrenith has mentioned. As for Evisceration, I would gear in terms of Accuracy > Attack > STR slightly greater then or equal to DEX. Keeping in mind Evisceration has the potential to crit, so the extra DEX may offset the advantages of STR.
The above does not take into account the bonuses gained from DEX when using Sneak Attack; however, THFs will still see more consistent and higher WSs from using a High Accuracy/High Attack build then stacking straight STR and DEX without regard to Accuracy and Attack. To achieve the best Accuracy/Attack/STR/DEX ratio for Dancing Edge and Evisceration is different for every THF and thus individual testing is required to see what works best for them.
