Aside from having a return pump in the basement sump that will overcome the head pressure, and still give you the flow you're looking for, and allowing room in the sump for drainage back down at powerloss - sounds like a wonderful idea.
I've never had a set up like what you describe. I've heard others here that have done just that, and maybe they can toss in a couple comments.
I will add this ...
Having such a large sump will allow you to add a lot of saltwater to your system.
This is a great thing in my opinion .. but adding that much new water to an "established" tank with fish may cause some shock or stress, especially if the water parameters, temperature, pH, specific gravity and such are not matched as close to the existing tankwater as possible.
You have some nice fish, and I would suggest when you set this up and turn it on, that you really pay extra attention to getting this new water to the same tested parameters.
Also if I was doing this, I would turn on the return pump for a few seconds until I saw water draining back to my sump, then turn it off for awhile, turn it back on for a few seconds, off again ... and continue this for a couple hours to sort of mix in the new water with your existing tankwater. A powerhead or two in the display tank might be necessary if you don't already have them.
You could have up to 100+ gallons of new water in this monster sump, more then doubling your system - very cool - but also a potential risk to any delicate fish you have in the 92 corner.
If you have the room, a nice saltwater mixing tank next to your monster sump would be a nice addition to this project. PVC piped with a pump to the sump, and a PVC drain from the sump to drain in your basement. Water changes would be a lot easier if you had this mixing station nearby.
That's about all I can think of right now.
Love to see some pictures of how you do this
