You want a filter that is big enough to handle the pump flow (not necessarily the maximum flow, the flow at 20-30 feet of head is about right) and have the combination turn your pool over in about 8 hours. You then probably want to upsize the filter one size or so. (The larger filter reduces pressure and reduces the number of times you need to backwash, saving on maintenance hassles). If you do this, I think you will come up with about a 48 square foot filter. A 70 square foot de filter is pretty big for your pool.

You may even be able to go with a 1/2 hp full rated pump if you go with an energy efficient model like the Northstar or Whisperflo.

You want to compare flow rates to size your pump, not hp as the hp will vary a lot for the same flow rate. For example the flow rate on 3/4 hp Northstar (Hayward's upper-middle range model) is about the same as the flow rate on Hayward's 1.5 hp SuperPump. Confusing, isn't it. A rule of thumb is to get the right size pump - a bigger pump will just eat energy and may actually not clean the pool as well - and upsize the filter.