All right, I finally got to use this guy the other night!
I did make a few last minute tweaks to his stats before inserting him into the adventure, changing the "extra standard action even if stunned" to "if denied actions, instead make a save".
The party was 15th - 16th level; present were a mage, a resilient battlemind, a cosmic sorcerer and a brutal scoundrel rogue.
They took Lurpask out, but it was a tough fight that ate up many of their daily resources. They rapidly discovered the damned if you do, damned if you don't nature of him. It was a very fun, enjoyable fight! They were scared of him, but I don't think any of the pcs ever dropped unconscious (they had a few potions of vitality and the rogue is multiclassed warlord; he had stand tough, which is a mass heal 15 hp without spending a surge power).
All in all, success! Thanks again to everyone who helped fine-tune his design.