To be fair you said Grandmaster, the Grandmaster is good but odds are good the Daemon Prince can still kill the Grandsmaster faster than the Grandmaster can kill the Daemon prince. A squad of Termies are a different kettle of fish entirely, though with the advantage of flight the DP still has a good odds of getting the drop on the Terminators. A squad of Terminators is more costly than the DP so If it can take out one squad and be banished in the process its done its job. I find Grey Knights to exspensive myself, Assualt Terminators with Thunder Hammers are the ticket better invunerable save to ward of monstorus creature attacks and if one Thunder hammer gets a hit then the entire squad is going to have a chance to fight next turn.
Enjoy multiple assault cannons while they last, as they will likely go back to one per 5 men in the next codex, but on the up side theyll probaly ditch the annoying Space Wolves HQ rule.
And yes that's one of my Daemon Princes, probably painted him some years back now, he's alright. Here's something more recent.
http://i221.photobucket.com/albums/d...s/100_0576.jpg
http://i221.photobucket.com/albums/d...s/100_0400.jpg