I dont think you want to go below 45k dps buffed in Act 2 on a wizard. On my monk I was very happy at around 30-35.
But the tricky thing is all those semi invul mobs (invis snake, jumping grenade throwers, etc). Act 3 you dont have those mobs as regularly so its sort of easier actually
Yeah I also found that Act 3 the packs are easier for me than some in ActII due to the fact that in Act III there is less space for them to run from me and kite my attacks.
I am going to be trying the Wizard solo build when I play again to see how that works out for me, will try for 6k armour 600 RA and then 30%+ crit chance
Other wise I will just stick to co-op play and be the glass canon