Sleep will still be tricky. Assuming you hit with sleep, how do you plan to close with Orcus to get the best use of Golden Mean? You pretty much want to be right next to him to get 5 rounds on him. Even if you aren't next to him you're going to be within reach of his attacks.
Closing with him is no simple matter thanks to difficult terrain aura of 6, but lets assume you have ways around that like teleporting. Now orcus is hit with sleep but he's merely slowed for a round before he gets to save. So he has a whole round of actions prior to making his save (including action point) to attack your wizard if he is within range. Can a wizard survive a +43 vs. fortitude death touch? Even after all of that, Orcus could easily teleport out of the golden mean before he has to make a save.
Of course there are ways around this, and probably better combos as using sleep, but it just doesn't look as simple as using 2 powers and orb mastery (oh and a potion). In fact there's a lot of risk in the above, so I wouldn't go so far as calling it 'broken combo' but good tactics.
And yes there are likely issues with orb mastery. A good HR would possibly be to cap it at -10 to saves.
