Actually, Niefelheims PD is under mediocre at best in my opinion -
jotun militia are pretty much useless, and while the jarl at PD20 is a very good thug even unequipped if blessed, it won't make much difference when he routs the moment the militia that amount of PD gives you dies.
Also their mages are expensive per research point in the magic-filled early era, so they'll either need some very lucky independent mage finds or simply HUGE amounts of gold. The good thing is that the skratti are awesome combat mages, singlehandedly they can even dispatch sc's solo when you hit high blood magic, and they can be turned into very efficient killing machines with proper equipment in werewolf form.
I agree with Agema, e9n4 or e9n6 bless is the optimal for the giants - possibly if you really want, add in some astral for late game astral power and some added magic resistance (the thing the giants really like is more MR when paralyze/soul slay starts to be the norm in the battlefield). Your Niefel Jarls and Niefel giants really benefit from the reinvig4 and prot4 from earth and the regen keeps them standing when the few odd hits get in or they spontaneously combust or whatever they like to take damage from.