Why not the 1 HP uprated (3/4 HP full rated) Whisperflo two speed? You only need 31 GPM for an 8 hour turnover. At 50 ft of head, it has 70 GPM, half speed is 35 GPM. You will get an 8 hour turnover at low speed and 4 hour at high speed. Also, you will not need to change the power as it runs on 115v.

One other thing, if it is a temporary situation, you could put in a slightly closed ball valve near the filter to increase the head loss. If you run the head up to 60 feet, the 1 HP uprated pump will flow only 60 GPM. Then when you get your new filter, remove the ball valve or open it up.