Not sure about gender size difference, I haven't sexed them as I feel guilty turning them on their backs as they think they're being fed and get really excited! There is one that is a lot smaller, but seems more lively then the others. My mum's named it Fawkes (after the Harry Potter Phoenix) I will have to take a look at sexes as I'm quite interested, for some reason I only ever have odd numbers in a litter! And always have more boys!
Also the ears are getting silly now! They're all starting to look like Dumbo, their ears are so out of proportion!