Interesting hearing what sizes people have their hamster pairs and groups in... I would be surprised if the boys didn't get along with something bigger than they have at the moment. They do run on their wheels lots but their absolute favourite thing to do is run about all over the cage, through and over all the toys (the cardboard box a tube of toothpaste came in has been a big hit).
It's like someone's been feeding them amphetamines and the wheels just aren't enough!
We've measured the room they'll be going in and I think we're (mostly him, I will be waving a hammer and trying to look helpful) going to construct something about 110/115cm by 55cm and have a separate unit to sit next to it to store food/substrate with the empty cage on top.
This won't be for a while though, there is more work that needs done in the spare room first and the wee men are still a bit too new to be moving them again so soon.