I think the ideal rotation is:
Ventura
Vargas
Volquez (Killer V's?!)
Duffy
Guthrie
More likely:
Ventura
Volquez
Vargas
Guthrie
Duffy
Volquez's peripherals lagged his performance last year, due largely to a significantly lower than usual BABIP and line drive rate than is typical for him, even in 2008 which was his best year by far. I doubt that is sustainable, but I sure hope so.