When upgrading OpenACS versions <= 5.8, one should use a Postgres 8.* (e.g. latest Postgres 8.4)
One should then dump the resulting 5.8 database, restore on a later Postgres version (any supported version, such as the one from your distro package manager should be fine) and proceed with the upgrade to 5.10.*
I just had experience about such an upgrade from an old OpenACS 5.4.* to 5.10.*, which was successfull (save the expected fallouts and adjustments).
