Anyone have this lens? I'm feeling a little stuck on which 70-300ish lens to get. Sigma and Tamron have 70-300 f/4-5.6 lenses available, both for sub $200 on Amazon. The nice thing about the Canon is the IS. I don't think I'm willing to splurge for the f/2.8 Sigma, f/4 or f/2.8 Canon (with or without IS), or f/2.8 Tamron versions that are close to $1000, this zoom range just isn't important enough for the stuff I do to justify the cost. But... before I buy a "budget" zoom I was hoping to get feedback from anyone who has tried it. It's in the $500-$600 range, so I'd need to feel like there was a clear advantage to it over the budget lenses. Any feedback is appreciated.