Another alternative to Winsor Newton are Raphael 8404 series. I honestly think these are better sable brushes. The quality of Winsor Newton brushes isn't consistent. You need to test each brush to see if it has the attributes expected from a top quality brush. When wet the brush should always spring back to it's original shape. If the brush keeps a crescent shape after you make a stroke then don't buy it. The ends on WN brushes also have a tendency to split. Not something you expect from a sble brush at that price. They should always have a point.
I am a production artist by trade and have alot of experience with painting media. The Raphael are the better brushes and the best part is their cheaper than WN.
Buy one of these sable brushes and if you take care of it, it should last you many years.