Nickyb, I have an SB600 and love it. Can't go wrong. If hes willing to lend you the camera you could always use both. Place a lens on each. That way if something goes wrong, you've got a backup plan.
I shoot pets professionally and have both lenses. I would say bang for buck the 50 is your friend, either 1.8 (plastic fantastic) or 1.4. I have also owned the 50 1.8 and the 50 1.4 - there isn't a HUGE difference between the two, though there is some. The downside of the 80 is that it's just so darn heavy, and really, getting a sharp focus on a moving dog at 1.2 is part miracle and part skill.
