The i386 and amd64 versions are built on separate machines, they will always have different times because they take longer/shorter time to compile the images, and those aren't build numbers, they are timestamps.
The update source shows i386, so there is no way that the amd64 images were there.
The GUI was probably sluggish because you didn't have working DNS, because the WAN was down. As for why the WAN was down, without more information it's impossible to say. Going from RC1 to RC3 is painless for almost everyone, we'd need to see a lot more information about your hardware or any errors you might have had in the logs or console when you were on RC3.