It can get complicated to decide on the best bang for the buck when it comes to GPU rendering. Especially with Nvidia the way they put out so many different cards with different clock speeds and memory specs. Just keep in mind that CUDA clock speeds and memory bandwidth play a huge role in rendering performance of the card along with core count. All the RTX cards have double the effective memory speed (14 Gbps) and use the newer GDDR6 standard. Memory bandwidth will help when you're trying to push large scene renders to the cores with lots of texture information. Some GPU render engines will offload scene textures and geometry to the CPU when the Vram memory limit is reached, but while this is good for getting things done it could slow down the render.

I would probably stick with the GTX 980ti for a while longer. At least until Blender comes out with the Optix enhanced rendering for RTX. By that time, the new RTX Super cards may come down in price and you'll get a great deal on a card.

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