Difference is , if the PSU dies and it's still under warranty, Corsair have legendary customer support so he'll have an easier life sorting it out. XFX have given people a lot of trouble in the past
I really doubt it matters whatsoever. Antec, Corsair, Seasonic and XFX all have good PSUs, and it's highly unlikely they'll fail even under a solid amount of stress. An 850W PSU will handle the system fine, and customer support probably won't even need to be involved.