Also take into consideration that NAT has been totally rewritten from 8.3 onwards. So the format you have been using up to 8.2 will change. This change also reflects to to the access-lists.
We are currently using 8.4(2) in most of our production environments. Also 8.4(3) in some of the newest ones.
As for the stability I can only say that we have not yet had any problems with the software version mentioned above.