Make sure it's focused (select your model and press f) on your target as well as that can affect the sensitivity when you get close. Making a new perspective will have no focus target so will use the default.
for a silouette, i would have just applied a black texture and turned it's self illumination up to 100. target weilding is cool, kinda like the v snap in maya. you can target weld edges too.
My feeling on it is that no smaller than 800 for basic layout. However pimp images should be as big as they can be to load fast and look good. Rick is spot on with the target audience thing. Just depends on who you're targeting.