DX to FX
I would say the investment is not worth the money. FX is great for portraits or shooting action and anything hand held in low light. Your field of work allows you to use a tripod and long exposure times, which allows you to keep ISO down which reduces the IQ difference between FX and DX to a very big effect. I can imagine that a D5300 (regardless of the cheaper body) would make more sense to give you lower noise at higher ISO settings (when needed) and also more resolution when needed.
hobby aviation photographer