If your rig is running over 80 mph, a nose cone with low water pickups can keep your prop from blowing out, and also allow you to raise the motor a little adding a mile or two an hour in most cases. However, if your boat is running somewhere well below 80, you don't need to worry about blow out in the first place, and a nose cone adds more length (i.e. more resistance) to the lower unit and usually will slow a rig down. Bottom line, if I was running over 80 I'd put one on for the simple reason of keeping from blowing out, if I wasn't running at least 75+ mph I wouldn't even consider one. I have one on my 210/250 combo, and best that I can tell is that it added about 1 1/2 mph. Mine is a Bob's grassmaster nose cone, btw.