Level 98 Poisonous Concoction Pathfinder^3.23

Notes

1. You ideally want 21 AoE radius, or preferably 22 (52%) to make certain all flasks hit single targets.

However, it's difficult to determine what is happening with flask overlap and AoE with PConc, because we are utilizing both GVS (which throws 4 + 1 flasks in parallel), and GMP (which throws 4 or 5 + 1 flasks in a fan configuration).
From my own testing it seems that 10 flasks with ~22+ AoE is a sweet spot, and the closer your target is the better. Charms can make up for the loss of our helm AoE enchant in 3.23, though it's a trade off against other very useful charm mods.

2. You also need to get some added Frenzy charge duration because of the reduced duration on the gloves and boots. The formula for how much you need to prevent the charges ever dropping is:

60% + (10 x #Frenzy Charges)%

That means you need 130% for 7 Frenzy charges (more for each additional charge), which is covered by +100% from Charge Mastery and 1 minor increased Frenzy duration node in the tree, 
plus at least one 10%+ increased Frenzy duration implicit on the rings. There are several other +20% duration minor nodes easily accessible if required.
You may need to select at least one more until you can run an Unnatural Instinct jewel, which picks up a node for free, and freeing up a skill point. Charms solve this particular issue in 3.23

2a. If you use corrupted Darkray Vector Dragonscale Boots with the +1 Endurance Charge corruption (recommended), you will need to carefully balance Increased Frenzy Charge Duration nodes to counteract the big 
Reduced Frenzy Charge Duration the boots have.

Bear in mind that Increased Skill Effect Duration on the Malevolence gem and some tree nodes (Damage Over Time Mastery for example) will increase the duration of the Aspect of the Cat cycle on your Farrul's Fur.
The effect of that is to require more Frenzy Charge duration to prevent the charges dropping. It took me ages to figure out what was happening with this. Benefit from my pain. You're welcome. Charms also solve this issue in 3.23

3. Don't forget Herald of Agony (a huge damage boost). Despair on Hit on a ring is now not nearly as good as Temporal Chains on gloves - even despite recent nerfs.

4.  Dash + Second Wind may seem a bit strange, as the cooldown conflicts with Withering Step. In practice (and you will get used to the timing), it is possible to use Dash toward the end of the cooldown.
The build is fast enough on its own, but it's much better to have it than not. Shield Charge is clunky, and can feel bad, but it also doesn't conflict with Withering Step's cooldown. It can replace Dash if preferred.

Special Note: Get the "#% Increased Duration of Ailments you inflict while Focused" mod on the helmet. There are several other possible mods, so ensure you search for this particular one.