Forum OpenACS Development: Optimum Connection Pool Size
However, as long as you never run out of database handles, I doubt there's that much performance impact of how many you have. There's overhead (particularly on the Oracle side) for each handle, so probably the fewer the better, without running out, but I don't know how much overhead there is per handle.
Note that with the db api in OpenACS 4.x, the 2nd and 3rd pools (traditionally called "subquery" and "log", although they no longer have those meanings), will be used only for the unusual queries which need multiple handles. Therefore, I suspect that the vast majority of your handles should be in the first "main" pool, not the second or third pools.