well magdrive makes a better quality pumps then rio. Sometimes a skimmer will perform better with a higher rated pump then it calls for. Search around on the net and see what pump others are using in that skimmer and i wouldn't be surprised if you find people running the mag 9.5.
After some Google of my own i see the recommended GPH flow rate is up to 900gph so you can base your pump choice on that number.