hmm, the dart is really good for closed loop applications, but I believe you may get better results with your application using a different pump.
The wattage and head loss that you'll suffer won't be worth it compared to some other pressure rated pump.
I think the panworld's do a good job with the pressure constraints in returns / seaswirls.
my recommendation would be to just do a regular return with two spray bar outlets (for even flow) and then do some kind of closed loop with the swirls.
The dart wouldn't be enough for the closed loop either, but it's bigger brothers like the hammerhead and barracuda would do great.
I know panworlds are kinda loud though, so beware. =/