Personally i don't like the idea of Dunlending cavalry. to me the only difference between the Rohirrim and the Dunlendings is Rohan's use of cavalry, and that is highlighted by Tolkien and GW alike. it would be an inaccurate depiction of the Dunlendings to mount them, as the mountain homes of the Dunlendings could not really support horses. but hey, don't let me spoil your fun.

Dunlendings are also described as using cavalry at the Fords of Isen. Most Dunlendings probably fought, however, on foot, with long spears, axes and other melee weapons (as with most self-arming forces, swords were expensive and therefore a rarity). Armour for most soldiers was light, but well-off warriors and chieftains likely made use of chainmail and were clad similarly as their Rohirrim counterparts.

Nordvolk are HUGE, bigger than everything else, they are MASSIVE, I have an army load all waiting to be painted up cos they are ace figures, but nothing matches them, the wizards in the range are even bigger 40-50mm in height, but It's fantasy so it's fine. Excellent range of figures but won't mix with anything else.

I have several packages of the Nordvolk vikings and they are on the large size but I think work really well against other fantasy figures if you want your barbarians to be a head taller then "regular" human sized opponents. I think works rather well but means you can't mix in other lines.