How far away do I need to be to comfortably watch a SuperScreen, without the picture looking all dotty?

That comes down to your screens pixel pitch and viewing distance. At ANSO SuperScreens we will help you select the best product for your intended audience.
As a rule of thumb, for outdoor screens with individual Red Green & Blue LED's, your screens pixel pitch equates to how far away in metres your audience should be. i.e. A SuperScreen with a 12mm pixel pitch will look best from 12m or further away.
When it comes to indoor and semi-outdoor screens with Red Green & Blue in the one LED package (or SMD LED's), 3/4 of your pixel pitch will give you a comfortable viewing distance. i.e. A SuperScreen with a 5mm SMD pixel pitch will look best from 3.75m or further away.