Also, one bit that might get overlooked a bit is what happens when the C'Tan dies.
In my game, his Str 10 AP2 explosion went out 19". That's like a vindicator shell that goes out in a 41" diameter circle. (Wider than half the board). Basically it seems like if an army of "Conventional forces" clusters up, you just jump the c'tan straight in there. Even if they kill him, he has a very good chance of annihilating the entire army after he dies. On the other hand, if the conventional forces spread out, it means he can jump to a flank, and avoid enough firepower to really threaten him as he rolls down the line. Basically it seems like your best bet is to go first, and have a "trick" that might take him out before he moves (like, 3 rune priests in a pod). No amount of "Regular stuff" will matter at all.