Serene Steelsaid: Nex is Lifesaid: Superior Dragon Dagger is already good.
I mean... kinda?
T78-T85 is a much more viable range for nearly every slice of content in the game. T70 is a little low, IMO.
EDIT: I can say that T88 might upset a balance via special attacks. Special attacks have increased accuracy and damage making it better than "T70" might seem when used as a sepc switch - look at Guthix staff!You'll get it when you deserve it.