This. Don't use Beersmith's predicted FG, it frankly blows and doesn't take into account mash temp, use of extract, etc. Even the yeasts attenuation rates are often screwy.
If you really want to know in advance your FG, you have to do a fast ferment: you take a small portion of wort, overpitch, ferment high and check the gravity of that after a few days. And even this test isn't always accurate because your real fermentation could very well attenuate less because you haven't overpitched or fermented high. It's more a measure of the overall fermentable sugars in the wort than a be all end all prediction of FG. FG stability for an extended period of time is pretty much the only way to know for sure the beer is done.