I am looking to buy a Minolta 75-300mm AF lens. When I looked at a lens review on Dyxum.com, they had two lenes that looked identical but had two diferent ratings. They had two product codes. The better one had a code of 2649-110 and the other 2606-100. How can I tell by looking at the lenes witch is the better lens? The only identifing marks I see are serial numbers.