death star = spartan.
I use Dart that because it give me an easier language in which to program and at the same time, it allow me to access the best of js library out there without having to rewrite them. I want Dart to make my life easier with large scale app just like small app. Also, I want Dart to take care of all the difference between language. I was a little bit disappointed when they decided to drop ie9, but I do understand that ie has always been a pain to work with. I will prefer that it provide a flag with which would specify which browser you want it for, and it will generate the code accordingly. I want that if I decide to use this or that function, Dart will generate the appropriate code to work on all platform.
As for speed, if I really need it, I will go with PNaCl or just go with an native app.