On needing an F2.8 lens, would that depend on what ISO he'd chose and what WB?
My answer is yes and no. As a general rule you want to go with the lowest ISO possible for the best image quality. A bigger aperture let's you do that. The higher you go on ISO, the more grain you'll see. However, many of the processors today will let you shoot at iso's i'd have never dreamed possible 10 years ago. It comes down to how big you're going to use the images, and how picky you or your customers will be.
I have a friend that shoots a Nikon ???-300 variable aperture at iso 1600-3200 to keep his shutter up at 1/2000 or so and f6.3. He then post processes the crap out of them. They look fine as long as you're not making posters out of the images.
WB doesn't enter into my equation for aperture. How is it a factor for you?
