Vision,
I think sequence pumps are awesome also. If you don't need a lot of flow, I would go with eheim but other than that sequence. I had a hammerhead and got it extremely quiet. Take a look at this thread,
http://www.manhattanreefs.com/forum/general-discussion/14845-sequence-pump-too-good-true.html
The snapper uses less watts than the dart but the dart gives you more flow.
As far as a dart with a tunze stream, heck nah it won't be too much in a 120. Especially if you decide to alternate between the two tunzes.
The reason I reccomend the snapper, is that his overflows may not be able to handle the flow on a dart.



