There seems to be a fair bit of confusion and misinformation surrounding the leaked Windows 7 RC build (marked as build 7100) and an earlier leaked build.
Rumors have been circulating that the latest build 7100 is identical to build 7077. Bottom line, it's not. Sure, they are similar, and it's true that build 7077 is the only beta build that you can "upgrade" to the RC release, but that's it.
Insiders have conformed to me that there are significant under the hood changes between the two builds, so move to build 7100 when you get the chance to complete your testing. Also, insiders tell me that it was build 7088 (which wasn't leaked) that finally became the RC build.
Will there be a second RC release? All indications seem to suggest that there won't be an RC2.