[Edi]

As far as both blesses go, remember that the bless weapon (whether fire or death) replaces any secondaryeffects from equipped (or intrinsic) weapons when the bless comes into effect, which means you won't get area damage from brands with a blessed SC if you have sacred SCs (such as Hinnom, Ashdod, Fomoria) etc) or thugs (the glamour nations, Lanka etc).

So if your strategy is based on thugging with national troops in the mid/late game, your best bet would be F8 for the +4 attack. D8 is more useful in what possibilities it opens up for you and sacred mages will benefit from the affliction bonus, slight as it is.