1) Infinity does NOT affect poison immunes.
2)Your poison gains tremendous damage if u use Trang shield + Trang belt and glove.
Trang-Oul's Wing
Defense: 175-189 (varies)(Base Defense: 50-64)
Required Level: 54
Required Strength: 50
Durability: 20
Chance to Block: 60%
(Necromancer Only)
+125 Defense
+30% Increased Chance Of Blocking
Poison Resist +40%
Fire Resist +38-45% (varies)
+15 To Dexterity
+25 To Strength
+2 To Poison And Bone Skills (Necromancer Only)
-25% To Enemy Poison Resistance (3 Items)
Put in another Psn facet for -30% !
Trang-Oul's Girth
Defense: 134-166 (varies)(Base Defense: 59-66)
Required Level: 62
Required Strength: 91
Durability: 18
16 boxes
+75-100 Defense (varies)
Requirements -40%
Cannot Be Frozen
Replenish Life +5
+25-50 To Mana (varies)
+30 Maximum Stamina
+66 To Life
Cold Resist +40% (3 Items)
Trang-Oul's Claws
Defense: 67-74 (varies)(Base Defense: 37-44)
Required Level: 45
Required Strength: 58
Durability: 16
+20% Faster Cast Rate
Cold Resist +30%
+30 Defense
+25% Poison Skill Damage
+2 To Curses (Necromancer Only)
You lose out on FCR that Arachnid offers, blocking and resists on the Arachs but marvel at the damage.

An additional -30% poison resist is a HUGE factor, combined with DW (psn faculted) you are looking at double damage figures after Lower Resist (even just lvl1).
Then the crowning glory for a poison necro has to be a 2 os + 2 necro skill + 20 fcr circlet with other goodies. 2 more facults for more FUN !
3) Max raise skeletons offers greater benefit before SM is factor in. 10 SM and 7 RS (assume NO +skills) create 206 hp and 28 dmg skeles but only 4. 17RS creates 336 hp and 23 dmg skeles BUT there are 7. In general raise skeletons create more resillient skellies and give you more of them.
4) As for Venom Lords, use Decrip and a Clay Golem. Slowing them down helps immensely, a Might merc with Pride will help the skellies in the killing speed while Might merc with Doom CA pretty much slooooows down the Venom Lords to impotent levels when combined with Decrip.