Get the smaller the pump if you can but I wouldn't be too concerned because a 1.5 HP AG pump is not usually that powerful anyway and not that over powered for a 150 sq-ft filter. I think the Xtreme comes with a Matrix and a 1.5 HP has a flow rate of around 53 GPM which puts the flow rate right below the APSP recommendations of 0.375 GPM/sq-ft so it should be ok.