As far as .cbr vs .cbz, it doesn't make a difference. I have opened both in CDisplay, and neither is faster than the other.
And if you save it as a ZIP file, it doesn't matter what you change the extension to. Any magazine I have scanned or compiled and uploaded was saved as a ZIP and had the extension changed to .cbr. So if anyone whines that one is faster than the other, tell them to shove it . I prefer .cbr simply because I see the extension as standing for Comic Book Reader, even if that isn't what it means.
ZIP, RAR, .cbr, .cbz; all the same pile of soft, pale faeces