I've been growing increasingly fascinated with how commander decks card's cmc and role can create a certain flow to how they play out.
With the Ur dragon's eminence trigger, the dragon primeval/chaos primeval all cost 5 mana.
This enables a sweet 1->3->5 ramp scheme to drop a primeval on turn 3 consistently.
On turn 4, with a land drop we can (attack + pay the trigger) + (play a 3cmc or less support card or another ramp spell)
I'm not sure where I'm going forward from that point, but this curve charts out the first 4 turns of a game nicely. Also I kinda like the vorthos angle of a dragon primeval ur dragon deck.