for SU modeling operations, the single-thread perfomance of the CPU is relevant only:

PassMark CPU Benchmarks - Single Thread Performance
Benchmarks of the single thread performance of CPUs. This chart comparing CPUs single thread performance is made using thousands of PerformanceTest benchmark results and is updated daily.
(www.cpubenchmark.net)
A mid-sized nVidia Geforce RTX is mostly sufficient, fortunately prices are dropping a little bit:

PassMark Video Card (GPU) Benchmarks - High End Video Cards
Video Card Benchmarks - Over 1,000,000 Video Cards and 3,900 Models Benchmarked and compared in graph form - This page contains a graph which includes benchmark results for high end Video Cards - such as recently released ATI and nVidia video cards using the PCI-Express standard.
(www.videocardbenchmark.net)
Improving performance of high-poly count models:
https://help.sketchup.com/en/sketchup/improving-performance
https://blog.sketchup.com/article/10-tips-for-modeling-large-design-projects