concerned mostly about having to compromise on the other carpets to get something really heavy duty for the staircase. Plus the fact that this piece of carpet will be isolated so much from the rest of the carpet that it might look out of place.
Ash, generally what makes the difference in heavy duty and extra heavy duty?
Does extra heavy duty mean they can't be as nice in terms of look and texture as carpets not rated as highly?
i.e. comparing commercial carpets with residential makes me think that the hardiest carpets look/feel poorer than the more delicate ones.
I find that a comment a little odd!
Why is there a compromise?.... you are considering timber which will be invariably more expensive than the finest carpets, so there's no reason to have to compromise on carpets! If the carpet on the stairs is bordered by timber, there's no reason to feel its out of place, especially if isolated from other carpets. So, there's no problem here at all!
Among the best carpets will be wool or 80/20 wool mix carpets, a minimum of 40oz, either woven construction or fusion-bonded. There are some magnificent axminster carpets that are made specifically for stairs. They are usually made in 92cm width (or sometimes 200cm) so there's virtually no wastage.
Does heavy duty mean tough and uncomfortable?... in a word, NO!