Gold is heavy sure, but its $/weight value is still much higher than basically any other cargo - the plane vs ship choice would be even more weighted towards the plane with gold than with most other cargo.
More detail: at current prices gold is $133k USD per kilo - at that price transport costs would be such a tiny fraction of the value of the cargo that it wouldn't make any sense to pinch pennies - you'd want to go with the absolute fastest, safest option.
So, railgun it is
High-end enterprise Xeon processors are worth more by weight than gold but Nvidia H200 processors are worth less. The Intel chips are worth 3-6x the Nvidia chips.