When it comes to rendering, more cores are always better, so the six core would probably be your best bet. Check out cinebench scores for each and that should give you a good idea of the CPU's rendering power.
I'm not sure if AutoCAD supports GPU rendering software, but that may be worth looking into. The i5 with a slightly faster GPU like the 1070 would probably give you way faster rendering speed, but not sure if it's supported in your apps. I think Octane Render has plugins for Sketch up, and maybe autocad. YOu just need an Nvidia (GTX gaming cards are fastest)https://home.otoy.com/render/octane-render/
Also, just saw you're using Vray, which also now supports GPU rendering (for the most part). Not sure if 3.5 is out yet for your apps, but they've fixed up a lot of the issues I had with it previously.
The other option that might be worth looking into is buying an off lease workstation. I know here in the States, you can find older HP z620 or Dell t5600's for $300-$600 depending on the specs. The 6 and 8 core versions are probably comparable to the Ryzen 1600x, and would beat a 1500x in render speed. If you can afford to get one of the 16-core models though, you'd have about 2000 in Cinenbench which beats out an overclocked 1800x or 6900k. I have two z620's I bought recently and use them as render nodes. They're solid machines and are workstation class, so they should last. Single core performance isn't the best, but your CPU renders will fly. And you can fit 2 10 series GPU's in there, so I also use them as GPU render nodes.