score:4
The following issues are to consider:
1) Heavy objects in your hand become a mortal projectile in case of emergency braking and other sudden movements. So you must keep the object in the overhead compartment or under the seat in front of you. Otherwise, it could break your neck, or somebody else's.
2) There is more room for movement in the overhead compartment, specially when empty. An unprotected heavy object might slide back and forward and bang against the walls of the compartment and get damaged. So the floor under the seat is the better place, provided it fits.
3) You should consider appropriate packaging for your laptop. While there are standard bags for laptops, some heavy movement might not offer appropriate protection. So generally it's recommended to add your own protection/padding, depending on the weight of the laptop. Bubble wrap is surely a good start, maybe not really practical for repeated packing and unpacking. There are special hard suitcases for heavy duty protection such as pelican or other.
Generally, the more you pack the object among other things (clothing etc), the better it is since it dampens any impact. Having the laptop without any padding inside a bag is definitely not recommended.