So the latest beta is apparently 64-bit to begin with. I've also noticed that it uses more RAM than the previous (beta) versions, which is quite disappointing. It now uses up even more RAM than Safari!! Has anyone else noticed that? I also don't like the the new "page loading" status because it doesn't tell much - seems like a copy of Chrome's too. I preferred how it was in the previous beta version. On the bright side though, it seems snappier than previous versions.
You need to remember it's still in beta. They generally don't worry a lot of RAM usage until their close to release. Though, with adding new features, it's quite likely to use more RAM even in the finished product.