Being totally serious mate, there's one area of the map for me by T mid where it drops to 190 for a second then it goes back to 250-300. Get between 300-400 in the indoor areas.
Dust II I get similar fps to ancient but never more than 400, Mirage and Overpass best maps for me with constant 280-340fps, goes to 400-450 in very low demanding areas like connector/lowers on both maps and especially indoors, just drops a bit by bathroom area on Overpass and long for some reason. I OC very stably to 4ghz, temps don't exceed 63 C, and I disable my even number cpu cores + core 0. My gpu is also a Palit version of the 1660 super and it performs insanely well. GTA V for example I get between 62-108 fps on max but motion blur turned off as well as grass detail at normal, averaging 85fps with benchmarks. Just hit the silicon lottery with my build. Looking to use my remaining parts to mine 24/7 once I've upgraded.
My mate has an i7 9700k and he is getting on average between 240-480fps on every map without it dipping, 1080p. He's having no problems on Ancient. Another mate of mine gets between 280-500fps on Ancient, got the exact same setup as me but he has 3600x and different RAM, 3600mhz GDDR5 8GBx2. Also gets noticeably more fps on other maps, easily 60-100 more. edit: Overpass and Mirage for him especially he gets loads of fps on his ryzen.