xdelta results:
666198016 CentOS-4.0-Beta-Binary-CD1.iso 635330560 CentOS-4.0-Beta-Binary-CD2.iso 661059584 CentOS-4.0-Beta-Binary-CD3.iso 662018048 CentOS-4.0-Beta-Binary-CD4.iso 444139520 CentOS-4.0-Beta-Binary-CD5.iso - 658491392 CentOS-4.0.rc1-i386-bin1of5.iso 611952640 CentOS-4.0.rc1-i386-bin2of5.iso 666099712 CentOS-4.0.rc1-i386-bin3of5.iso 663128064 CentOS-4.0.rc1-i386-bin4of5.iso 360095744 CentOS-4.0.rc1-i386-bin5of5.iso - 522078044 disc1.delta - 144119972 diff 584136615 disc2.delta - 51193945 diff 630595579 disc3.delta - 30464005 diff 613272303 disc4.delta - 48745745 diff 322226619 disc5.delta - 121912901 diff - Total: 396,436,568 bytes
I don't have the bandwidth resources to publish the diffs but to save ~400megs of bandwidth, it'll be worth it to people who have beta isos.
Rob