1.6W should look pretty good in an indoor venue this side of a football stadium provided its smoked or hazed properly.
Insanity has had a 1 Watt whitelight laser for some time for professional shows so he can probably advise you on the kind of venues size wise it will work well in.
Outside yes its going to be far less impressive because of the problems of smoking / hazing the area. As Doc said, green is by far the brightest colour, so outside will give you the best visibility.
Just to throw another option in the pot, one thing you could do is get a Spectrum for indoors and then pick up a CuBr for outside (OVERHEAD ONLY - THEY'RE PULSED) use. They're relatively cheaply available second hand (although you do need big scanners) and will give you multiwatt powers far in excess of 2W.
This is a 10 Watt rated(?) CuBr we had at UKLEM last year (bearing in mind its pulsed its probably nearer 40 Watts+:
