There's a bit of forced perspective in the second photo - Melly's not that big - but you can get an idea of how close in size they are now. I've tried using my bathroom scale to see if they're the same weight yet (weighing myself, then again holding each cat) but it's too hard to tell. Geoff has a digital kitchen scale that might work, so I'll give that a go and report back.
And for those who requested a video of the sleeping, twitching, chirping Mellybean, I will see what I can do. She tends to regain consciousness when I get too close with the camera, which I may need to do for the mic to pick up her noises. But I will try!