I dont think the Staffy x Pat would be the best at rabbiting, they take a few in cover but getting them to retrieve the rabbit without shreading it will be another downfall.
Like Dogs n native said above, a lurcher would be your best bet and there is alot of crosses to choose from, in my opinion you need to be looking at the Collie based, Beddlington Based or GWP based lurchers, from working lines all will do you a good job.
Let us know how you get on.
Dave,