Well, the important thing to remember is that Category 5 storms are really unstable and that it's very hard for a storm to remain at that level for long. So if it is a Cat. 5 that far from land, there's a decent chance of it losing some strength before making landfall. After all, only 3 storms to hit the US since 1928 were Cat. 5 when they hit. In fact, several of the stronger storms I've been in (Isabel in 2003 and Hugo in 1989 come to mind) were Cat. 5 at one time or other and were then downgraded before making landfall.
Either that or we're going to see a US hurricane strike that rivals Camille for intensity.