IMO, if you had to choose from a great GPU, or great CPU, put your money in the CPU. As seen in the post Jeff referenced, CPU core count seems to be more important than GPU, as most of TCAD's functions are mainly CPU dependent, even when rendering.
You do benefit from a good GPU, but the gains realized aren't as great as with CPU improvements.
TC 21 Deluxe, TC 20 Platinum, TC 2015 Platinum, TC 2016 Platinum, TC 2017 Platinum
i7- 3770 Ivy Bridge 3.4 GHz, 16G Crucial Ballistic, ASRock Extreme 4, EVGA 1060 SSC, Windows 10 Pro 64 Bit