Size and top end are the easy bits, what a stud dog is really doing is the real question...
Bonny blue bitch that... Personally, I wouldn't give two fecks about type, size, colour or any other crap BUT try to find a stud that can catch what you want to catch, in enough numbers...
That bit seems to be missing from your post... For me, in a worker, it'd be the only thing required ?