Erik, as I know some vendors allow user two erase modes: page erase and block erase. For example, Atmel introduces the block as 8 pages. So when you erase chip in block mode then it takes not 30s but about 6 seconds (due block erasure takes some more time than page one: 12ms vs 8ms).
BTW, which chips you have looked on? Is DataFlash(r) not trademark of Atmel only?
Ok
a) Chip erase is the only one that interest me in this case.
b) Flash is for data, not code.
c) I have looked at6 about every flash available in thi size and the 'dramatic' diffrence is the chip erase time which, in most cases, is NOT specfied as a parameter, but stated in the "general description"

Erik