Killing 4 orbs should be no problem regardless of talents. 5 is still pretty easy if you utilize procs well and save a 3-orb DP for that wave. 6 is also doable without any help, but it could go either way if you have a dry spell with procs and can't get 2 more orbs during the 5th wave (I hate when people kill my orb before I can get off a SW: Death). We can hardly ever get all 6 orbs down on the 6th wave, so we've been sticking to 5. I don't really see any need to do more than that unless you're just looking to inflate your DPS for logs or something.