The g-list is the 'grown list' of bad sectors. The g-list itself only contains the addresses of blocks or sectors that o bad during operation. These are then mapped and recorded in the drives parameters in the SA area ( translation table) to point to what were 'spare' sectors when the drive left the factory. The g-list itself doesn't contain any data, but the pointers to the sectors that are bypassed. The chances of the bad sectors containing any information are the same as any other sector that has ever been written to. Clearing the g-list means that those sectors will now be readable, or at least one hardware device will read the g-list and hunt down just those sectors for cloning. Bu since they were bad enough at some point to be marked, what are the chances it will be readable now. Secure erase come in two flavors of implementation. Killdisk does not implement secure erase, SE is a low level command, there is a freeware console app out there that will implement it. If I read the documentation on it correctly, the first version of SE does not process p and g list sectors ( The p-list is the permanent list of bad sectors, those that were marked bad at the factory and should never be used) I beleive Enhanced SE does process the g-list.
Secure Erase info and utility from here
http://cmrr.ucsd.edu/people/Hughes/SecureErase.shtml
Seriously tho, if your only interest is cleaning this one drive, replace it and physically destroy the one with your data on it. If it's a learning experience then have a blast!!
Also you could run killdisk on the drive, then try some of the recovery tools so you can see what exactly is left. or do a zero wipe and use winhex and do a boolean searcg for hex values that are not 0, that would show you any unwiped sectors.
Have fun!