we normally have been running the 1.5" spacers:
UTV Crap
you will gain 3" overall width. negatives is just spacing the weight of the wheel and tire off the spindle. steering components, etc.
if youre going to be jumping your teryx a whole bunch and trying to clear the 40'ers we dont recommend them, haha.
the wider stance is always a plus for stability, makes its less likley to tip over, can it still tip over, YES, but you have less of chance.
we run them on all 4 wheels. get the best stance you can.