I've just put my young beardie in a 4'x18"x18" viv and he loves the space. I was worried about him catching his food but, hey, no probs there, not with his speed. Better than telly.
1.0.0 Bearded Dragon/Killing Machine : Roddy
1.0.0 Crested Gecko : Merlin
0.1.0 Gargoyle Gecko : Amber
1.0.0 Yemen Chamelion : Bruno
0.1.0 Shrieking Cockatiel : Chip