Too much would be relavent to what it does to the inhabitants of the tank. The more flow you can give the tank the better off it will be. Don't guage the results simpley from the numbers. If the 800ish GPH
does not have a whirlpool effect and the fish are not struggling to swim about the tank, that amount of flow is quite beneficial to the tanks health.
You will also find that the flow of the HOB
will not contribute that much on the whole if it contains media. The media clogs quite quickly and reduces the flow. Finding different angles for the PH
will also help in creating caotic currents that will help eliminate dead spots and circular flow.