I like 1+2 :-D Use the Tee, but put a ball valve in both directions, then you have complete control of flow!

Also, not sure if your problem is completely pump/sump fow rates? It could simply be sump "capacity". when you start the sump return, water rising in the tank is perfectly normal, it needs to rise to a point where it seeks a level based on return flow, and overflow+standpipe flow rate, "Then" the water starts to return to the sump, which could now be "Dry" because it is undersized. You can always pour more water into the sump to get the system to reach equilibrium, but this causes a BIG problem! If you loose power, or turn off the pump, your sump will quickly overflow and you will have several gallons of saltwarer on the floor.

Ideally, your sump is large enough to reach this equilibrium, and still have reserve capacity (empty space at the top) to hold the water that will drain when the pump is off, and until the siphon on your return breaks.

Does this make sense?