The Robert Sorby diamond section parting tool is a great choice for a parting tool.
Its diamond profile means there is less material in contact with the material at any one time, this means there is limited heat build up due to the reduced surface contact, and also means there is less chance for it to bind mid cut.
The narrow 4.75mm (3/16") cut also means not too much material is removed, so those expensive or difficult to get timbers are not being wasted each time they are cut off.