Thank you for chiming in Colin--i've read some of your past posts and have tended to find them interesting and/or informative. Yes, Qiviut is interesting stuff too, but way too expensive to either buy the fiber, and i imagine quite hard to raise the animals! The average micron count of Qiviut and Angora Rabbit fur however, is quite similar, and they are both more truly hollow fibers, and so they should have a very similar warmth rating.
I've read some interesting studies (albeit somewhat oldish) which compared traditional/Native Artic clothing compared to more modern mountaineering and military clothing and found that the traditional stuff worked better as far as keeping you warm in these truly cold, Artic conditions. These usually use Carbiou which apparently has very densely packed, hollow fiber fur.
I'm no expert by any means, and while i do know that "loft" is quite important in warmth, i don't think it's the only major factor either. It is important for Down, since Down primarily relies on a combination of it's very, very fine fibrils and naturally lofty nature to provide excellent warmth.
But i'm thinking that even if the Angora rabbit fur does matt and felt some, even though the loft will be decreased, it won't be as much an issue as it would be with say Down. Reason being because of the rarish combination of rather hollow fibers and rather fine diameter size.
Most synthetics for example, either try to minic Down by re-creating the micro like fibrils (fibers) of Down, or they use hollow fibers, or they combine the two. However, the hollow fibers that synthetic makers use, still aren't that fine. It's apparently hard to create both hollow and micro sized fibers at the same time, especially any that have any natural resilance like Angora does.
A side note: It's interesting that Angora rabbits have not been adapted to truly Artic conditions like Qiviut, and yet they still have such extremely warm, warm fur. I've thought about this, and two reasons become apparent. Wild rabbits typically as a species have very lean bodies with little fat reserve or buildup, and two, they tend to be rather small animals, and so even in moderately cold conditions they would need very warm fur to stay warm enough, wheras an Arctic Musk Ox (Qiviut), has the large, thick, bulk mass and greater fat reserves plus the super fine, downy and hollow fiber undercoat.