your pga / work area size parmeter seems to be standart so they shouln't be the reason for that problem.

But because you said that you got this error when you get close to the 1gb i'm alost sure that the reason for it is the bug 3130972. So I recommand you either to upgrade to 9.2.0.6 or to apply the one off patch.

Increasing _pga_max_size will not solve the problem but, from my experience, rather increase the probability that you hit that bug. However once you applied the patch and if you often do large sorts/group by or large hash joins you may got a much better performance if you increase _pga_max_size to 1 or 2 GB.