Maximum memory for various freebsd releases

Looking through the various release notes I see that one thing thing 
that is rarely mentioned is the amount of physical memory supported, 
or any tuning that may be required to run more than some amoutn 
(should it be necessary to change some table sizes etc.).

If anyone has that information I'm looking to know if it is possible 
to run 768GM of ram on an 8.0 machine and a 10.0 machine, and if not 
in the default configuration, whether there are any changes to the 
configuration that would allow this.

Julian