RE: Redhat 6.2 to 7.0
I'm not sure as to the specifics of the effects of an upgrade (as far as what files get over written, which ones are left that shouldn't be). I always tend to think a clean install is "better". From practical experience, however, I can say that I've upgraded several times (ex: from 5.2 to 6.0 and from 6.2 to 7.0) on different machines and have never had any problem. The only issue I've ever encountered was not having enough disk space. And that was my fault.