I have thought that my self over the years. I reckon a 1/4 lab 3/4 grey, would make good lurcher[brain,speed,good coat+feet, and should make good retriever. pity you dont see them about.???
I had that very cross 20 years ago mate, it was a fairly useful dog took to water like a duck, and caught plenty of feathered game, strange thing was it had a bite like a great white, it was the hardest mouthed dog i ever owned. I gave it to my mate who really bonded with it, and it turned out to be a real charlie killer, just shows when breeding theres no surefire way of knowing what you may get.