I think it would be worthwhile to consider the parts seperately to get an idea of what each can handle. I will give you a theoretical approach for the estimating, hopefully saving you a bunch of experimentation.
I would use the laminar flow equation to estimate what flow you will get. <I know the flow won't be all laminar, but the turbulent equations are too hard to use, and we are estimating anyway!> This is the equation:
Flow = (Pi x r^4)/(8 x n x l) x dP
r = radius of your pipe, l = total length of pipe, n = viscosity of water (constant), dP is the driving pressure - or how high your water level is to drive the given flow.
Instead of trying to figure things out by plugging in the values directly, I would suggest taking an observation & using the equation as a proportion. This would account somewhat for the elbows, constrictions, & other imperfections in your piping that causes turbulence.
Since the Dursos appears to be the bottleneck, we will consider that first.
You need to measure what driving pressure is needed to handle your pump flow. To do that, you need to add more water to the sump so your pump won't run dry, and measure how high the water is in your tank once you get everything balanced. dP is the distance from the top of the water to the inlet. < Yes, you will have more water than is safe .... so make sure you do this outside if possible .... or be ready to plug both standpipes before you turn off the pump & drain out excess water in the tank. >
Once you know that height (we know that it is at least 2" above your overflow top), you can figure out what flow the system can handle at your planned water levels, like this:
Since r, n & l are unchanged, you can simpify the equation to:
Flow = dP/R ...... R = resisitance of the setup.
Using 2 sets of equations for the 2 flow conditions, combining the 2 equations ....
Flow1 / Flow2 = dP1 / dP2
Say Flow1 is your Mag 24 at 2000gph, and your driving pressure dP1 is 4", and you have only enough height in the setup to give a driving pressure of 1" (dP2) ....
Plugging everything in gives you a Flow2 of 500gph .... this is what gph
your setup can handle. <I would not run a pump right at the edge of system capability .... cut back 25-50% to handle the invariable glitches during operation.>
Of course, I am only guessing at the numbers by looking at the pics. Try with real measurements & see what you get. The Dursos should be able to handle more than 500 gph
, even at 1" of head height .... so you might be able to tune the system for better performance <eg - changing the air hole size>. If you can't get the Dursos to handle an acceptable flow rate, you'll have to consider using an open channel design <in an open channel or full siphon setup, dP is the height between your overflow & your sump .... so can handle much higher flows>, or re-designing the overflow. The other option - dropping the height of the Dursos to gain more head height is not safe with the siphons taking water from the bottom - since the minimum water level would be too low & you'll flood the sump with a power out.