whippet grey would be loads faster but the colli grey will give you stamina and brains but sometimes colli crosses have too much brains which can be good and can be bad sometimes but whippet greys will give you a 100% every time it runs but they can run out of steam quick compare to the colli cross but they still very good dogs if i had a choice i would go for a whippet grey lyk because i lyk how they run and how keen they are atb Top Lamper