Perhaps you can't decide which processor to buy, you can make a decision by looking at the AMD Ryzen 9 3900 Cinebench r23 score single and multi core test and understand is it a good processor or a bad one to buy, how powerful is this CPU. Here is all information from Cinebench r23 benchmark. A careful review of all the specifications, to make it easier to read, is made by the table. After looking at the data this test and video, you already be able to figure out do you need to buy AMD Ryzen 9 3900 or not.
Although it should be understood that all the figures in the article above do not mean that taking them into account you should fully trust a simple quantitative comparison. Better to watch benchmarks video and read the opinion of real owners of AMD Ryzen 9 3900 before deciding buy this processor or not.