Lowering gears or extending flaps comes with limitations. Given the answer of this question I suppose the limit speed for full nose down is about 325 kt. My question is: what were the limit for all positions (visor down but nose full up, nose in take off position, nose in landing position, any other position I don't know)?
After checking the systems chapter on the nose, it turns out a dual uplock failure would limit the drop to 5° (see updated answer). If it is just one uplock that failed, the nose/visor should hold, but reducing the speed is out of caution.
As for the speed limits, here they are from the aircraft limitations section of the manual: