Dude, the dart is WAY overkill for a 90 gallon tank... I mean, sheesh! I have a 210 and wouldn't consider running one of those on it...
(Although I'll be running an Ampmaster 3000 on it soon; different story, though. I'll be throttling mine back for better efficiency.)
I have a 1200 GPH pump on my 90. It's about 900-1000 GPH by the time it gets to the tank. I'm also running an eductor on the output. It's a GENX MAK4 pump. Overall, I love that pump. Been running for probably 7 years now and it's been fabulous (note to self: have it rebuilt!).
You could get away with much smaller pumps IMO. I'd go with an external one, regardless, because of heating issues.
There's a lot of discussion regarding "too much flow" through a sump. Most of the flow that people are adding these days is via either closed loop or internal pumps (Tunze's, Vortech, whatever). Me, I'll probably be going with lower flow through the sump (and even less through the fuge) although with a 2 inch drain (on my 210) I could push a ton of flow... I also have a wavemaker and 2 Tunze 6100's, so I have plenty of flow regardless.
It's been said that any more flow than your skimmer can process is wasted flow. Perhaps you may want to keep that in mind, as well...