6" vs 8" hyperfan for 315 cubic feet?

6" = 315 cfm
8" = 710 cfm
tent will have LED lighting
Which CFM rating is more optimal? The 315 CFM is right on the dot. Or is it best to get bigger than what you need and operate the fan at lower speed? Thanks

also adding a carbon filter. I just learned that filters can decrease fan efficiency by 25% therefore will be going with 8" fan.