Replying to Promaster lenses???

ok....so ive been waiting on my Nikon nikkor af 80-400mm f/4.5-5.6 ed vr d lens for about 2 months (it been on back order). so my dealer offered me any "equivilant" promaster lens....same zoom ext. he told me this this a accually a better lens (faster) and that it retails for more than the Nikon. so....just wondering anyone has anything to say or a review about the promaster lens. im not sure about it because i know that Nikon makes a good lens. so i dont want to take the chance without knowing for sure.......thanks