The cheviots have the highest quality of any of the british breeds - that was what all the "tweed" was woven from and a whole Scottish woolen industry was built on. Only the specialist wool breeds like merino have higher quality wool.

The copper issue is funny - yes it can be toxic but they sometimes can't do without it either. The terminal sire breeds have a lower tolerance to copper, especially the "continental" ones like texel, beltex, rouge. At the same time most of the UK sheep population gets routinely injected with copper because the soil is really deficient - way, way more so than most of the prairies. We would inject pregnant ewes with 2mls copper sulphate in January and again in March with an April lambing flock. If you didn't do that you would get a condition called sway-back in the lambs - they are born with spinal defects that literally makes them sway and stagger about. If they are born with this condition you may as well hit them on the head as they'll never amount to anything. I saw a jacob lamb on an acreage near me recently that had swayback - the owner wanted my opinion on why it kept staggering about so don't believe all you read about sheep not needing copper.