A scrubbed ISO is still 4.37 GB (single-layer games at least)
It's just able to be compressed into a .rar or whatever and be a smaller size since the dummy data is turned into 00's.
A cISO is basically a .rar file. It's a compressed ISO, without the 00's.
Yes, you can turn a scrubbed ISO into a cISO. There's no difference but file size, really.