To create a first cross hybrid twixt a herder and a running dog,..,..I would always prefer to use the Greyhound or purpose bred type of up and at em,..hare killer as opposed to a pure whippet....
The whippet blood is great and can always be added at a later date ,.if required....
However,..if the chosen end product is required to be a wee'un,..I always favour starting off bigger,..then by dint of a further mating,..reduce the overal size of the hybrid.
This would be my own method of utilising most of the Herding breeds,..
As for toughness, mental attitude, etc,...it would be naive