If your 120-300 is 7 years old, it's more than likely the version before the Sports version, right? While the optical formula is similar, the build quality and QA inspection process are vastly improved. I absolutely love both my Sigma 120-300mm f/2.8 Sport and my Sigma 150-600mm f/5-6.5 Sport. And while it may sound like it, I'm not actually sponsored by Sigma. wink
Scott Flaherty