So I'm looking over the Vicious Opportunist and comparing it to the standard Rogue Sneak Attack. Given the number of feats and Rogue Talents which allow you to increase the damage from Sneak Attack is the VO really any better?
I see the VO is added to crit damage like Power Attack, that is certainly nice (especially with a keen / high threat weapon like the Rapier). I see VO can be used outside of the normal 30ft range for Sneak Attack, that too is pretty nice. And I see VO can be triggered anytime the enemy is suffering from a disabling condition such as fatigue, sickened, etc and that leads to being usable more often, that too is nice.
So while it breaks down to being (basically) a + 1 per level in damage, does this really compare to a TWF rogue who at 10th level is laying down an extra 5d6 sneak damage + weapon, enchantments, feats, etc 3 times per round?
Bare in mind, I'm not questioning the extreme end of the "what if" multi-classed theory crafting here, I'm only comparing 2 single classed rogues at 10th level, with other factors such as equipment and player experience being comparable.
With rule of averages d6 being 3 1/2 per die, the edge goes to SA until lvl 5 (10 1/2 dmg - 10 dmg) and then the edge goes too VO at 6, even at 7, Vo at 8+. Lvl 10 would be 17 1/2 vs 20. But that is averages, can always yatzee that 5d6 for 30 and own VO. Really pretty close, but VO edges out by the numbers.
Sounds like it is really something of a wash and more of a question of play style and if the player / dm would prefer the more predictable results from VO or the "burst damage" potential from the SA dice.
On the flip however, the additional conditions under which VO can be triggered, additional range at which it can be used and the fact that it is applied during critical hits (similar to power attack) sounds like it would surpass SA just because of how often it would come into play over a 6 hr game session.