I don't know however I would imagine that
the only limit is the amount of configuraiton
memory that you have. You could move the config to flash then you would have more:-) Eventually you
would of course run out of memory.
It has been rumoured, but I don't see why it
might be the case, that performance decreases
with NAT table size.
It is possible to limit the number of NAT
translations. Tha max limit value is 4G.
i.e. 2 ^ 32. By default it is not limited.
Try it out time.
Would be easy to use a spreadsheet to
fake up a big config. Cut/paste/crash:-)