Just picked up a brand new 3900XT to replace my 3600X, and I am seeing almost no improvement in single-threaded benchmarks. I'm getting low 2700's in Passmark single-thread CPU, and an absolute max of 506 in R20 single-thread. Also, if I enable PBO in bios, the cpu actually boosts even LOWER than if I just leave it on Auto, and runs single-thread benchmarks considerably slower than my 3600X.
I'm running the latest bios for my motherboard, f20b, that was released this week. I've loaded optimized defaults and started over, I've cleared CMOS from the motherboard jumper, and I've reflashed several times. I have the latest chipset drivers and I am running the Ryzen Performance power profile in Windows 10.
Temperature isn't an issue, I'm running a 240mm AIO watercooler as a case intake, and even in the highest load conditions it doesn't even get to 70C.
Over the weekend I tried a second 3900XT from a different store, and had almost exactly the same results. The CPU runs the fastest in all benchmarks (considerably slower than even a 3900X) with optimized bios defaults loaded. As soon as I enable PBO, it becomes somehow even slower, on par with or slower than a 3600X.
Motherboard: Gigabyte x570 AORUS ELITE bios ver. f20b
CPU: AMD Ryzen 9 3900XT, 240mm ASUS AIO
PSU: Corsair 850W 80+ Platinum
System Memory: 32GB Dual Channel 3200 MHz
Windows 10 19041.330