What does slax have when you boot it?
Does it have: GParted, ddrescue, myrescue, partimage, photorec, testdisk, ... other usefull recovery tools?
I think Slax is more a small desktop system, not a rescue/partiton system.
XWindow system, KDE desktop with K-Office, Internet browsing, e-Mail, Instant messaging, CD/DVD burning and ripping, Audio and Video encoding, Multimedia players, all and even more is included in Slax.
I think that Victor also find it to big (189MiB).
It seems a nice distro to me, but I think it is not suitable for the goal of UBCD. You can probably easily include it yourself because it probably will also use isolinux.
Parted Magic size is 44 MiB (4 times smaller). We can extend it with antivirus software and other tools if we want. Make a 7zip archive of the files that the program needs and place it in /pmagic/pmodules
See the antivirus topic for examples of the 7zip archives, It is made for Parted Magic 2.2. In the new version of Parted Magic 3.0, the files should be inside a /usr folder first, because it unpacks the files in /. Parted Magic 2.2 unpacks files directly in /usr.