AFAIK the reeds have infinite "innate" quality - and when you collect them, hardcap is determined from combination of your Survival and Sharp Tool quality (and possible type of Sharp Tool.) It may not be a simple "average the values."
It was average when they were released, i personally verify that and wrote that on wiki. But i guess that was rebalanced, wiki is open source calculate the formula if you can and add it. Last time i played i remember that reeds have quality spots pretty much as everything but still depends on your tool.