CPU or GPU ? :
Twinmotion is based on Unreal Engine and makes only moderate use of CPU (although faster is still better, if one can afford it) against intensive use of GPU.
Twinmotion performance is dramatically determined by GPU capabilities. Two cards might give slightly better performance but one high-end card is a much better choice.
Both GPU speed and video memory capacity are important. The best devices on the market at the moment are the following :
Windows : Nvidia Quadro P6000 (expensive), then GeForce GTX 1080, GeForce GTX 2080 Ti, the new Titans then the GeForce GTX 1070 Ti (quite cheap). Also, always keep your video drivers up-to-date.
Mac : Radeon Pro Vega 64 16 Go, Radeon Pro Vega 56 8 Go, Radeon Pro 580 8 Go.
You'll find a videocard benchmark on this website to compare these ones, considering that Twinmotion would need at least a graphic card of 6,000 points to work fine.
4 cores is recommended, having more will only benefit some specific operations (like importing a terrain) but shouldn't make much of a difference regarding the speed of the software.
In short: beyond 4 cores, prefer faster CPUs against CPUs sporting more cores.
Have enough RAM so your operating system won't need to swap data on disk. 16 GB sounds like a bare minimum if your projects are big and/or you need other CAD software running simultaneously.
Host your project and files on a fast SSD for best input/output experience (reading and writing files).