Any added feature does reduce frame rate. The RTX 2060 still should win all your frame rate tests given it has more cores and so on.
RTX 2060, 1660 Ti and then plain 1660.
CUDA Cores 1,920 1,536 1,408
RT Cores 30 0 0
Tensor Cores 240 0 0
If your budget allows for the 2060, that would be my choice since you may change your mind later and you can't add RTX later.
I'm looking to upgrade from the 750 ti and considering the two mentioned and I have to ask if I'm imagining things or are these 2 GPUs pretty close spec wise only the RTX does Ray Tracing ? I don't care about the Ray Tracing and from what I understand with that function turned on it decreases the frame rate ? Opinions and suggestions please ?