The 980ti is a good deal. The 980ti performs about 30% better than the 1650 Super. When comparing the 980ti with the 1660ti, they are both about equal, with the 980ti performing slightly better in some games, and the 1660ti performing slightly better in others. The 1660ti costs $270, while the used 980ti costs $200. I feel like the 980ti is the logical choice. I personally got lucky a couple of months ago, and found a MSI manufactured 980ti that has a Corsair liquid cooler on it, and came with a factory-overclock for $190, and to me, it was an obvious choice. One thing to note is that the 980ti takes so much power it is ridiculous (250 watts max). The 980ti will be able to handle newer titles at 1080p @ 144hz, 1440p @ 60hz. Also notable is that the 980ti was the first card with DX12, and was the first "real" 4k 60 fps card.
A question I have for you is what CPU and power supply do you have?