your still thinking as a demo buyten.
necro spell damage coeficients on all spells are very low.
as much as you stack magic damage after you get 1400ish magic damage any more magic damage wont make big impact on your dps; its why despoil the soul 8 stack inst op for necros, if you gave that buff to any other magic damage class you would create a monster especialy true for pom's who seem to have realy high spell coeficients.
like i think i mentioned to you already inteligence stacking+will of sublime+crit rating+crit damage is what increases dps considerably for necros, you can eficiently crit more often and crit harder
also more pets up the more dps you do, so single target wise sw to get parasitic souls will be more eficient then getting death god all the time
for example on that erlic geared necro on test live with no aa's i didnt get a single crit on plague swarm in like 15 minutes of sw uisng lich+tome etc, while on my "real" necro full t4 with full aa's i crit often on all spells, in sw my flesh to worms on that build crits for 750-800 all the time and i get average 5+extra ticks from blasphemy, wich by the way just having that buff up does more dps then casting plague.
and in multiple target situation you can substancialy increase your dps by doting everything that moves and sw spaming icestrikes+blasphemous ruin with deathgod or crit damage buff, and that is independant of spec.
if your realy keen of discovering the true power of infestation eficiency do it in a raid like last boss w1 or seruah in w2, or even in pvp minigames for that matter :P.