This is my current CEDH list, Its about a 4-5 since it does have 2 card infinite combos in the deck and multiple win-lines in between with infintie mana and Urza. I wanted to make it more "Urza themed" but had to keep it high power to keep up with my current play groups.
1 Winter Orb 1 Urza's Bauble 1 Static Orb 1 Orb of Dreams 1 Mesmeric Orb 1 Torpor Orb 1 Worn Powerstone 1 The Mightstone and Weakstone 1 Trinisphere 1 Chalice of the Void 1 Sphere of Resistance 1 Tangle Wire 1 Thorn of Amethyst 1 Unwinding Clock 1 Sensei's Divining Top 1 Candelabra of Tawnos 1 Mox Opal 1 Chrome Mox 1 Mox Amber 1 Mox Diamond 1 Lotus Petal 1 Sol Ring 1 Mana Vault 1 Basalt Monolith 1 Grim Monolith 1 Smokestack 1 Realmbreaker, the Invasion Tree 1 Maskwood Nexus 1 Mishra's Bauble 1 Ashnod's Altar 1 Crucible of Worlds 1 The One Ring 1 Grindstone 1 Mindslaver 1 Lion's Eye Diamond 1 Isochron Scepter 1 Mystic Forge 1 Rings of Brighthearth 1 The Millennium Calendar 1 Mycosynth Lattice 1 Darksteel Forge 1 Howling Mine 1 Liberator, Urza's Battlethopter 1 Platinum Angel 1 Laboratory Maniac 1 Thassa's Oracle 1 Mishra's Self-Replicator 1 Sai, Master Thopterist 1 Painter's Servant 1 Leveler 1 Stasis 1 Rhystic Study 1 Mechanized Production 1 Power Artifact 1 Thought Lash 1 Force of Negation 1 Force of Will 1 Counterspell 1 Dramatic Reversal 1 Abjure 1 Mana Drain 1 Urza's Mine 1 Urza's Tower 1 Urza's Power Plant 1 Urza's Workshop 1 Urza's Factory 1 Urza's Saga 1 Urza's Cave 1 Karn's Bastion 1 The Tabernacle at Pendrell Vale 1 Lotus Field 1 Lotus Vale 1 Mishra's Workshop 1 Vesuva 1 Scorched Ruins 1 Strip Mine 1 Wasteland 1 Boseiju, Who Shelters All 1 Academy Ruins 1 Ancient Tomb 9 Island 1 Polluted Delta 1 Scalding Tarn 1 Flooded Strand 1 Misty Rainforest 1 Prismatic Vista 1 Karn, Scion of Urza 1 Karn Liberated 1 Karn, the Great Creator 1 Karn, Living Legacy 1 Enter the Infinite 1 Urza, Lord High Artificer