I am torn between paying $1200 for a Nikon 17-55 or $400 for the Tamron 17-50. I currently have a Tamron 17-50 for my D80 which is my second shooters camera now. I now have a D300 and am curious as to what others are using. The Tamron is a great lens for a great price. Is it worth me paying 3 times that for the Nikon or sticking with the Tamron? Thanks!