Wait, Sturgia works? I was almost sure that snow isn't implemented in the game - I get no movement speed penalty through snow as any faction. By contrast, something like the Battanian cultural perk does work: moving through Forests gives you a -x.xx 'Forest' movement penalty, roughly a third of which is offset by a +y.yy 'Feats' bonus.
As for Khuzait, it doesn't work the way it should, just found out today. As of 1.4.0 at least, it gives your army a 'Feats' bonus of 10% of your 'Base' movement speed, for free. Doesn't matter if your army is all infantry (contrary to what the cultural perk blurb says). So typically, Khuzaiti culture is worth 0.4 to 0.6 movement speed, depending on your army size.
It's possible that Khuzait Lords have been running around with 0.4-0.6 movement speed advantage this whole time.