As for raiding unholy is your best to go with, i've notice myself that ever since i left blood i did sacrifice alot of dps but in a twist unholy aoe burst damaged seems to work better ( im avrg. 3-6 top dps with a GS of 5100+) but never let anyone tell you how to play your toon ,experiment with the trees and find your taste but fyi unholy is fun and alot better survivibility. and as for your diseases there is a wicked macro so you can spam and do wicked dps here is the macro:
#Showtooltip
/castsequence reset=combat/target/6 Icy Touch, Plague Strike, Pestilence
/startattack [harm]
this will turn 3 buttons into a single multi infection and save you the lost of dps and if time right can keep you from havin to spam like crazy and focus more on your dps.
