I don't kno' nuthin' 'bout dem Necs but wat I do kno' is dey aren't da bestest nukers in dis hear game. Also to help people maybe give you a better response give the level of your toon. Charisma might help your healing but I think the only casters that get a dex mod to their damage spells are Wizzy and maybe Alch.
ok basically infectious stream is a direct damage spell that does base dmg of 142. the modifier on this spell is dexterity and its a 30% modifier. this basicaly means you take your dexterity (lets say its 100) and then take 30% of that. so 30. then add 142 and 30 together and so your new number is 172 this varys so with 200 dex you would do 202 dmg. these type of modifiers are on all your spells. BTW necros get a really nice undead spell at 24. 346 base dmg with 60% wis modifier. so you need only 100 wis to nuke for 400+. GL