Use the 6.5 for primary and the 5 for secondary after bubbling drops to once every 30 seconds or so. Krausening is not as big an issue, though there is some. Oxygenation is not really a factor in the primary, so the 6.5 is fine. Why risk wasted mead?
"Brew or do not brew, there is no try."
Bottled and Drinking: Maibock, EdWort's Apfelwein, Traditional MeadUp Next: Cherry Melomel