I run a collie greyhound first cross, very useful bitch, but i was lucky and she has thrown quite racey and is quick off the mark, but for what i do bushing rabbits in small fields i would opt for something with a bit more speed, i also find if there isn't much action going on she gets bored quickly and finds something else to do like find a stick to play with.
Many years ago i used to go out with a pair of real old blokes doinga bit of bushing and ferreting and they used to sware by there whippet/greyhounds for catching the bolting rabs, can make very good dogs, but like steve said earlie