I think you can find out the info about the readers from the Mobileread wiki:
https://wiki.mobileread.com/wiki/E-book_Reader_Matrix
Kobo Touch has 2 gigabytes of storage, from which about 1 GB is reserved for operating system, thus giving 1 GB free for user.
Sony T1 has same amount of storage, but about 1,3 GB is free for user.