What is safe for negative g's? How about staying within the design limits of the aircraft? For normal category that would be -1.52g and for utility category that would be -1.76g.
Hop in a 172 and slam the yoke all the way forward and you will most likely exceed -1.52g's.
I agree that it is important to keep things simple. How about this: At Va, you can still exceed design characteristics with control inputs.