don't trust anything the manufacturer says about their pumps. All pump applications are different. ie head pressure, hose diameter, duty cycle, longevity, efficiency, heat output, etc. If I were you, hook up everything then pump some water up through your plumbing. See how long it takes to fill up 1 gallon of water from your sump to your tank. That will be your rated gph once you do your math.
Personally for me the quiet one is a piece of junk (like most submersibles used as a return pump. I bought it and it didn't last more then 6 months with a 3 foot head pressure running through 1" pipes. Most pumps just aren't designed for a lot of pressure and usually what I notice the most is that on the cheaper pumps, the coils tend to get burnt out. Since you already got the pump just try to reduce as much pressure to the pump as you can by running fatter tubes. Eventually this pump will break on you and you will replace it. I've been through many submerssible pumps of all kinds of ratings. when your sick of replacing due to coil failure, you will get an external pump so just be prepared for it. I got the Iwaki and never turned back. Its been a super reliable pump so far and I've never had any problems with it.