IMO the Khan in TOS was a lot less dangerous than the Khan in nuTrek. In TOS in the byplay where the crew were teasing Spock about the great qualities of Khan, it was shown that he liked to control the 'sheep' not destroy them. In Space Seed it didn't sound like Khan was really out to destroy anything just gain power over the Earth from his 'brothers'.
Except when Kirk defeats his attempt to take over Enterprise - at that point, Khan heads to Engineering and wires the ship to explode.
Just as, in TWOK, in his last moments he activates the Genesis Device to destroy Kirk.
Just as in STID, when defeated, he targets Starfleet with his disintegrating ship to cause as much damage as he can.
"I'll say one thing for him, he's consistent."