Out of curiosity I rebuilt the archives planning to test the unpacked integrity using Beyond Compare. Here are the stats:
Original Folder size: 802,014,370 bytes (1101 files, 137 folders)
WinRAR 3.50 archive size: 737,140,770 bytes
Time take to build: 39 minutes
TestResult (WinRAR): Frustratingly Good (Sod's law at work)
WinZIP 9.0 SR1 archive size: 753,862,116 bytes
Time taken to build: 5 minutes
TestResult (WinRAR): Good
I don't know why it worked this time ... I did exactly the same thing the other day 3 times and every time the RAR file had bad CRC results. Trouble is it then won't let you extract beyond the bad file (it just says the RAR file is damaged).
To be fair on the poor compression results the folder set consisted of lots of files, many of which were already compressed with ZIP, RAR, CAP, GIF or JPEG. There were also a lot of PhotoShop files, PDF files, .EXE files as well as a lot of text/HTML etc. Given the number of precompressed files the compression rate is to be expected.
It is interesting though to look at compression times for these files !!!
It is also interesting that the ZIP file tested a lot quicker too.