My mate bred a litter of wheaten greyhounds a year or two back, he kept three back but one of them unfortunatley died. THe two dogs he has at the moment are the bees knees and have took all quarry with ease on plenty of occasions. He also owns the father, in my opinion would give most a dog in this country a good run for there money, with drawing in mind. i myself have a young bullcross pup at the moment which is coming on well.
As to a lot more bull crosses not making the grade compared to wheaten crosses, i think its just the sheer number of bullcrosses out there compared to the wheaten