That is a massive fuge for a 75 gallon system.
Are you doing a planted set up as a display next to your main display? Normally I set my fuge to get 25% of my total water flow but I have mine set to gravity drain.
Are you pumping water from DT to fuge or from the sump?
Are you going to run the fuge output to the display tank or the sump?
The standard rule of thumb for return pumps is 4-5x your volume or roughly 300gph with your current set up if you get a pump capable of 500 - 600gph or so you could run a second line off of it (with a valve to meter the water flow) to feed the refuge and then gravity feed back to your sump. Some may disagree with me but I think a fuge should be a low flow zone serving to creat a seperate part of the eco system that will incourage the growth of algae and filter feeders (feather dusters, sponges, etc...)
Sorry only idea right now (without a better picture of what your doing how things are positioned etc..) that does not require you to buy 2 matched pumps and valve the outputs on both to match the flow.
I was toying with the idea of a planted fuge on display next to my tank but with a possible move in my near future haven't really worked out the details so let me know what you come up with and how it works please.