I agree with 7° for takeoff. This removes ground returns (unless the hills are very high) but will still paint weather. As you climb, lower the tilt until when in cruise, you're looking down slightly (edge of closest ground return about 60nm in front) to pick up the lower sections of big buildups. And if you're really "looking" for weather, not just big CBs, put the gain up to full until you find it, then lower gain to help avoid it. Quite often small buildups that produce harsh bumps won't show very well in auto gain.