.......A lot of people are concerned about the speed of this lens. ......
Two things will really allay these fears if you think about them.
1. The lens' VC is terrific. I've consistently gotten blur-free images down to 1/30 at 600mm.
2. Modern DSLRs are so good at higher ISOs these days. The fear of noise shooting at 400 or 800 or even 1600 should be eliminated from your mind.