Just thought I'd share my recent experience. I've been using a 3/4 hp pump for the last 2 seasons. My original filter was a hayward 74 sqft cartidge. It was a cheap garage sale find. This year after start up I just couldn't get my head pressure down, it runs 20 psi after cleaning. I picked up a used clear ways filter I believe about 320 sqft on craigslist and installed yesterday. The filters are still a bit dirty, I hosed them down but they could use a good soaking. Head pressure hovers at >5psi now. I have 4 jets that blow and can even run my poorman's deck jets at the same time. Both skimmers flow with eddys inside them and my diver dan cleaner is jetting across the bottom. Its like the pump has twice the flow. I know it makes sense, we cut the resistance to flow considerably, but still I'm amazed at what a difference it makes.