Worth is something only YOU can determine.
What is your budget?
Have you overclocked your 4790K?
If not, you are leaving some 30% cpu performance on the table.
Some games are cpu limited, and some are graphics limited.
If you run your game at low settings, does your fps improve?
If it does, that indicates that your processor is capable of running a better graphics card.
A GTX1080ti is a significant jump in graphics performance.
A I7-9700K and a RTX2080 super is about as good as it gets for gaming.
You will also need a z390 based motherboard and ddr4 ram.
What is the make/model of your 750 and 850w power supplies?
If they are of good quality they will run any modern graphics card you can afford.
Do not worry about 850w, the psu will only consume the power demanded of it, regardless of the max capability.