I've had pretty good luck with 12 ga. Winchester Xpert High Velocity 2 3/4" steel loads with 1 1/16 oz. of #3 shot at a velocity of 1,550 fps.
Or you can go with the 3" with 1 1/8 oz. of shot at the same velocity.
Hunting over my Brittanys I haven't found the need for the 3 inchers. I fact this year I will probably be using my new Citori White Lighting 16 ga. more with the Federal Ultra-Shock steel loads with 15/16 oz of #4 shot.