I did some experiments with the help of Bigeye giving me viewers feedback
screen res 1028*768, xfire detail = not broadcasting, my ingame FPS = 98
screen res 1028*768, xfire broadcast detail = Low, my ingame FPS = 67, viewers rating of video visual quality = 2 (low no. to high, higher the better)
screen res 1028*768, xfire broadcast detail = med, my ingame FPS = 65, viewers rating of video visual quality = 5
screen res 1028*768, xfire broadcast detail = high, my ingame FPS = 60, viewers rating of video visual quality = 3
screen res 1440*900, xfire detail = not broadcasting, my ingame FPS = 95
screen res 1440*900, xfire broadcast detail = med, my ingame FPS = 40, viewers rating of video visual quality = 7
screen res 1440*900, xfire broadcast detail = high, my ingame FPS = 25, viewers rating of video visual quality = 6
conclusion, use xfire broadcast detail of medium with the highest screen res you can
Here are 3 screen shots with the map zoomed (3 settings)
This gives a good idea of the viewers experience of streaming, its youtube quality