be more specific: i use 8051 and need 32 or 64kB of external ram.
you need be more specific:
exact derivative
clock speed

One more question: memory organization. Which to choose? numberx8, numberx16.
Does the organnization only affects the programming (bank selecting)?
No bank selection since yoy say 32-64k.
numberx8, I assume you mean data bus width, the '51 has an 8 bit bus.

Erik